diff --git a/autotests/export/latex/001-4-latin-OT1.lyx b/autotests/export/latex/001-4-latin-OT1.lyx
new file mode 100644
index 0000000000..1a99945f2f
--- /dev/null
+++ b/autotests/export/latex/001-4-latin-OT1.lyx
@@ -0,0 +1,623 @@
+#LyX 2.3 created this file. For more info see http://www.lyx.org/
+\lyxformat 523
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\begin_preamble
+\usepackage{wasysym} % provides \DH, \dh, \Thorn, \thorn
+\ProvideTextCommandDefault{\TH}{\Thorn}
+\ProvideTextCommandDefault{\th}{\thorn}
+
+\DeclareTextAccentDefault{\k}{T1}
+\DeclareTextSymbolDefault{\NG}{T1}
+\DeclareTextSymbolDefault{\ng}{T1}
+%\DeclareTextSymbolDefault{\DH}{T1}
+%\DeclareTextSymbolDefault{\dh}{T1}
+%\DeclareTextSymbolDefault{\TH}{T1}
+%\DeclareTextSymbolDefault{\th}{T1}
+%\DeclareTextSymbolDefault{}{T1}
+\end_preamble
+\use_default_options false
+\maintain_unincluded_children false
+\language english
+\language_package default
+\inputencoding utf8
+\fontencoding default
+\font_roman "default" "default"
+\font_sans "default" "default"
+\font_typewriter "default" "default"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc false
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\use_microtype false
+\graphics default
+\default_output_format pdf2
+\output_sync 0
+\bibtex_command default
+\index_command default
+\paperfontsize default
+\spacing single
+\use_hyperref false
+\papersize default
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 1
+\use_package esint 1
+\use_package mathdots 0
+\use_package mathtools 1
+\use_package mhchem 1
+\use_package stackrel 1
+\use_package stmaryrd 1
+\use_package undertilde 1
+\cite_engine basic
+\cite_engine_type default
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 0
+\branch na
+\selected 0
+\filename_suffix 0
+\color #faf0e6
+\end_branch
+\index Index
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 3
+\paragraph_separation skip
+\defskip medskip
+\quotes_style english
+\dynamic_quotes 0
+\papercolumns 1
+\papersides 1
+\paperpagestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\end_header
+
+\begin_body
+
+\begin_layout Subsection*
+1) Basic Latin
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+\begin_inset space ~
+\end_inset
+
+ 0 1 2 3 4 5 6 7 8 9 A B C D E F
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+20 ! " # $ % & ' ( ) * + , - .
+ /
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+30 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+40 @ A B C D E F G H I J K L M N O
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+50 P Q R S T U V W X Y Z [ 
+\backslash
+ ] ^ _
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+60 ` a b c d e f g h i j k l m n o
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+70 p q r s t u v w x y z { | } ~
+\end_layout
+
+\begin_layout Subsection*
+\paragraph_spacing single
+2) Latin Extended
+\end_layout
+
+\begin_layout Standard
+Makros 
+\backslash
+DH, 
+\backslash
+dh, 
+\backslash
+DJ, 
+\backslash
+dj, 
+\backslash
+NG, 
+\backslash
+ng, 
+\backslash
+TH, 
+\backslash
+th not available in the OT1 font encoding.
+\end_layout
+
+\begin_layout Standard
+Accent makro 
+\backslash
+k not available in the OT1 font encoding.
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+A0   ¡ ¢ £ ¤ ¥ ¦ § ¨ © ª « ¬ ­ ® ¯
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+B0 ° ± ² ³ ´ µ ¶ · ¸ ¹ º » ¼ ½ ¾ ¿
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+C0 À Á Â Ã Ä Å Æ Ç È É Ê Ë Ì Í Î Ï
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+D0 Ð Ñ Ò Ó Ô Õ Ö × Ø Ù Ú Û Ü Ý Þ ß
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+E0 à á â ã ä å æ ç è é ê ë ì í î ï
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+F0 ð ñ ò ó ô õ ö ÷ ø ù ú û ü ý þ ÿ
+\end_layout
+
+\begin_layout Subsection*
+3) Latin Extended-A
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+100 Ā ā Ă ă Ą ą Ć ć Ĉ ĉ Ċ ċ Č č Ď ď
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+110 Đ đ Ē ē Ĕ ĕ Ė ė Ę ę Ě ě Ĝ ĝ Ğ ğ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+120 Ġ ġ Ģ ģ Ĥ ĥ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ħ
+\end_layout
+
+\end_inset
+
+ ħ Ĩ ĩ Ī ī Ĭ ĭ Į į
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+130 İ ı IJ ij Ĵ ĵ Ķ ķ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ĸ
+\end_layout
+
+\end_inset
+
+ Ĺ ĺ Ļ ļ Ľ ľ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ŀ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+140 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ŀ 
+\end_layout
+
+\end_inset
+
+ Ł ł Ń ń Ņ ņ Ň ň ʼn Ŋ ŋ Ō ō Ŏ ŏ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+150 Ő ő Œ œ Ŕ ŕ Ŗ ŗ Ř ř Ś ś Ŝ ŝ Ş ş
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+160 Š š Ţ ţ Ť ť 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ŧ ŧ
+\end_layout
+
+\end_inset
+
+ Ũ ũ Ū ū Ŭ ŭ Ů ů
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+170 Ű ű Ų ų Ŵ ŵ Ŷ ŷ Ÿ Ź ź Ż ż Ž ž 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ſ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Subsection*
+4) Latin Extended-B
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+180 ƀ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ɓ Ƃ ƃ Ƅ ƅ Ɔ Ƈ 
+\end_layout
+
+\end_inset
+
+ƈ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ɖ Ɗ Ƌ ƌ ƍ Ǝ Ə
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+190 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ɛ Ƒ
+\end_layout
+
+\end_inset
+
+ ƒ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ɠ Ɣ ƕ Ɩ Ɨ Ƙ ƙ ƚ ƛ Ɯ Ɲ ƞ Ɵ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1A0 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ơ ơ Ƣ ƣ Ƥ ƥ Ʀ Ƨ ƨ Ʃ ƪ ƫ Ƭ ƭ Ʈ Ư
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1B0 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ư Ʊ Ʋ Ƴ ƴ Ƶ ƶ Ʒ Ƹ ƹ ƺ
+\end_layout
+
+\end_inset
+
+ ƻ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ƽ ƽ
+\end_layout
+
+\end_inset
+
+ ƾ ƿ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1C0 ǀ ǁ ǂ ǃ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+DŽ Dž dž LJ Lj lj NJ Nj nj 
+\end_layout
+
+\end_inset
+
+Ǎ ǎ Ǐ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1D0 ǐ Ǒ ǒ Ǔ ǔ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ǖ ǖ Ǘ ǘ Ǚ ǚ Ǜ ǜ ǝ Ǟ ǟ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1E0 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ǡ ǡ
+\end_layout
+
+\end_inset
+
+ Ǣ ǣ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ǥ ǥ
+\end_layout
+
+\end_inset
+
+ Ǧ ǧ Ǩ ǩ Ǫ ǫ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ǭ ǭ Ǯ ǯ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+1F0 ǰ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+DZ Dz dz
+\end_layout
+
+\end_inset
+
+ Ǵ ǵ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ƕ Ƿ
+\end_layout
+
+\end_inset
+
+ Ǹ ǹ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ǻ ǻ
+\end_layout
+
+\end_inset
+
+ Ǽ ǽ Ǿ ǿ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+200 Ȁ ȁ Ȃ ȃ Ȅ ȅ Ȇ ȇ Ȉ ȉ Ȋ ȋ Ȍ ȍ Ȏ ȏ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+210 Ȑ ȑ Ȓ ȓ Ȕ ȕ Ȗ ȗ Ș ș Ț ț 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ȝ ȝ
+\end_layout
+
+\end_inset
+
+ Ȟ ȟ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+220 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ƞ ȡ Ȣ ȣ Ȥ ȥ
+\end_layout
+
+\end_inset
+
+ Ȧ ȧ Ȩ ȩ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ȫ ȫ Ȭ ȭ
+\end_layout
+
+\end_inset
+
+ Ȯ ȯ
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+230 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ȱ ȱ
+\end_layout
+
+\end_inset
+
+ Ȳ ȳ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ȴ
+\end_layout
+
+\end_inset
+
+ ȵ ȶ ȷ ȸ ȹ 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+Ⱥ Ȼ ȼ Ƚ Ⱦ ȿ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Labeling
+\labelwidthstring 00.00.0000
+240 
+\begin_inset Branch na
+inverted 0
+status collapsed
+
+\begin_layout Standard
+ɀ Ɂ ɂ Ƀ Ʉ Ʌ Ɇ ɇ Ɉ ɉ Ɋ ɋ Ɍ ɍ Ɏ ɏ
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\end_body
+\end_document
diff --git a/autotests/export/latex/en-th_utf8.lyx b/autotests/export/latex/en-th_utf8.lyx
new file mode 100644
index 0000000000..12958db477
--- /dev/null
+++ b/autotests/export/latex/en-th_utf8.lyx
@@ -0,0 +1,455 @@
+#LyX 2.4 created this file. For more info see https://www.lyx.org/
+\lyxformat 573
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\begin_preamble
+\AtBeginDocument{\usepackage{fonts-tlwg}}
+\end_preamble
+\use_default_options true
+\maintain_unincluded_children false
+\language english
+\language_package default
+\inputencoding utf8
+\fontencoding auto
+\font_roman "lmodern" "FreeSerif"
+\font_sans "default" "FreeSans"
+\font_typewriter "default" "FreeMono"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc false
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\use_microtype false
+\use_dash_ligatures true
+\graphics default
+\default_output_format default
+\output_sync 0
+\bibtex_command default
+\index_command default
+\float_placement class
+\float_alignment class
+\paperfontsize default
+\spacing single
+\use_hyperref false
+\papersize default
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 1
+\use_package esint 1
+\use_package mathdots 1
+\use_package mathtools 1
+\use_package mhchem 1
+\use_package stackrel 1
+\use_package stmaryrd 1
+\use_package undertilde 1
+\cite_engine basic
+\cite_engine_type default
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 1
+\use_minted 0
+\index Index
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 3
+\paragraph_separation indent
+\paragraph_indentation default
+\is_math_indent 0
+\math_numbering_side default
+\quotes_style english
+\dynamic_quotes 0
+\papercolumns 1
+\papersides 1
+\paperpagestyle default
+\tablestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\end_header
+
+\begin_body
+
+\begin_layout Subsection*
+Thai
+\end_layout
+
+\begin_layout Standard
+Up to version 2013/03/31 v1.8, Babel’s “thai.ldf” changes character categories
+ and the definitions for up-/dowcasing of letters (catcode, uccode, lccode)
+ 
+\series bold
+globally
+\series default
+.
+ As a result, high bit characters come out wrong in the output.
+ UTF8 encoded characters are not parsed but interpreted as byte (=character)
+ sequences:
+\end_layout
+
+\begin_layout Quotation
+
+\backslash
+languagename 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+languagename
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Quotation
+
+\backslash
+familydefault 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+familydefault
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Quotation
+
+\backslash
+f@encoding 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+makeatletter
+\backslash
+f@encoding
+\backslash
+makeatother
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+and the 
+\emph on
+Latin supplement
+\emph default
+ characters are written
+\end_layout
+
+\begin_layout Quotation
+A0   ¡ ¢ £ ¤ ¥ ¦ § ¨ © ª « ¬ ® ¯
+\end_layout
+
+\begin_layout Quotation
+B0 ° ± ² ³ ´ µ ¶ · ¸ ¹ º » ¼ ½ ¾ ¿
+\end_layout
+
+\begin_layout Quotation
+C0 À Á Â Ã Ä Å Æ Ç È É Ê Ë Ì Í Î Ï
+\end_layout
+
+\begin_layout Quotation
+D0 Ð Ñ Ò Ó Ô Õ Ö × Ø Ù Ú Û Ü Ý Þ ß
+\end_layout
+
+\begin_layout Quotation
+E0 à á â ã ä å æ ç è é ê ë ì í î ï
+\end_layout
+
+\begin_layout Quotation
+F0 ð ñ ò ó ô õ ö ÷ ø ù ú û ü ý þ ÿ
+\end_layout
+
+\begin_layout Itemize
+catcode 11 or 12 means, the characters are directly passed to the font and
+ come out wrong when the T1 font encoding differs from latin9.
+\end_layout
+
+\begin_layout Itemize
+uc/lccode changes prevent up/downcasing of high-bit characters
+\begin_inset Newline newline
+\end_inset
+
+(lösen → 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+MakeUppercase{
+\end_layout
+
+\end_inset
+
+lösen
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+}
+\end_layout
+
+\end_inset
+
+, LÖSEN → 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+MakeLowercase{
+\end_layout
+
+\end_inset
+
+LÖSEN
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+}
+\end_layout
+
+\end_inset
+
+).
+\end_layout
+
+\begin_layout Standard
+
+\lang thai
+Setting the text language to Thai:
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+
+\backslash
+languagename 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+languagename
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+
+\backslash
+familydefault 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+familydefault
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+
+\backslash
+f@encoding 
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+
+\backslash
+makeatletter
+\backslash
+f@encoding
+\backslash
+makeatother
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+
+\lang thai
+Non-ASCII characters are mis-represented because the bytes are passed to
+ the (Thai) font as-is:
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+A0   ¡ ¢ £ ¤ ¥ ¦ § ¨ © ª « ¬ ® ¯
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+B0 ° ± ² ³ ´ µ ¶ · ¸ ¹ º » ¼ ½ ¾ ¿
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+C0 À Á Â Ã Ä Å Æ Ç È É Ê Ë Ì Í Î Ï
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+D0 
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+
+\lang thai
+Ð
+\end_layout
+
+\end_inset
+
+ Ñ Ò Ó Ô Õ Ö × Ø Ù Ú Û Ü Ý 
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+
+\lang thai
+Þ
+\end_layout
+
+\end_inset
+
+ ß
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+E0 à á â ã ä å æ ç è é ê ë ì í î ï
+\end_layout
+
+\begin_layout Quotation
+
+\lang thai
+F0 
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+
+\lang thai
+ð
+\end_layout
+
+\end_inset
+
+ ñ ò ó ô õ ö ÷ ø ù ú û ü ý 
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+
+\lang thai
+þ
+\end_layout
+
+\end_inset
+
+ ÿ
+\end_layout
+
+\begin_layout Standard
+Example text in Thai.
+ Emphasizing works, if 
+\begin_inset Quotes eld
+\end_inset
+
+fonts-tlwg
+\begin_inset Quotes erd
+\end_inset
+
+ is loaded 
+\series bold
+after 
+\series default
+Babel:
+\end_layout
+
+\begin_layout Quote
+
+\series bold
+\lang thai
+ภาษาไทย
+\series default
+ หรือ 
+\emph on
+ภาษาไทยกลาง
+\emph default
+ เป็นภาษาราชการและภาษาประจำชาติของประเทศไทย ภาษาไทยเป็นภาษาในกลุ่มภาษาไท
+ ซึ่งเป็นกลุ่มย่อยของตระกูลภาษาไท-กะได สันนิษฐานว่า ภาษาในตระกูลนี้มีถิ่นกำเนิดจ
+ากทางตอนใต้ของประเทศจีน และนักภาษาศาสตร์บางส่วนเสนอว่า ภาษาไทยน่าจะมีความเชื่อมโ
+ยงกับตระกูลภาษาออสโตร-เอเชียติก ตระกูลภาษาออสโตรนีเซียน และตระกูลภาษาจีน-ทิเบต
+\end_layout
+
+\end_body
+\end_document
diff --git a/autotests/export/latex/en_ja_platex.lyx b/autotests/export/latex/en_ja_platex.lyx
new file mode 100644
index 0000000000..8c9e8710ff
--- /dev/null
+++ b/autotests/export/latex/en_ja_platex.lyx
@@ -0,0 +1,125 @@
+#LyX 2.4 created this file. For more info see https://www.lyx.org/
+\lyxformat 572
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\begin_preamble
+
+\end_preamble
+\use_default_options false
+\maintain_unincluded_children false
+\language english
+\language_package default
+\inputencoding utf8-platex
+\fontencoding auto
+\font_roman "lmodern" "IPAexGothic"
+\font_sans "default" "IPAexMincho"
+\font_typewriter "default" "DejaVu Sans Mono"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc false
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\use_microtype false
+\use_dash_ligatures true
+\graphics default
+\default_output_format default
+\output_sync 0
+\bibtex_command default
+\index_command default
+\float_placement class
+\float_alignment class
+\paperfontsize 12
+\spacing single
+\use_hyperref false
+\pdf_title "LyX's Additional Features manual"
+\pdf_author "LyX Team"
+\pdf_subject "LyX's additional features documentation"
+\pdf_keywords "LyX, Documentation, Additional"
+\pdf_bookmarks false
+\pdf_bookmarksnumbered true
+\pdf_bookmarksopen false
+\pdf_bookmarksopenlevel 1
+\pdf_breaklinks false
+\pdf_pdfborder false
+\pdf_colorlinks true
+\pdf_backref false
+\pdf_pdfusetitle false
+\pdf_quoted_options "pdfencoding=pdfdoc, linkcolor=black, citecolor=black, urlcolor=blue, filecolor=blue, pdfpagelayout=OneColumn, pdfnewwindow=true, pdfstartview=XYZ, plainpages=false"
+\papersize default
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 0
+\use_package esint 0
+\use_package mathdots 1
+\use_package mathtools 0
+\use_package mhchem 1
+\use_package stackrel 0
+\use_package stmaryrd 0
+\use_package undertilde 0
+\cite_engine natbib
+\cite_engine_type authoryear
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 0
+\use_minted 0
+\notefontcolor #0000ff
+\index 索引
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 3
+\paragraph_separation indent
+\paragraph_indentation default
+\is_math_indent 1
+\math_indentation default
+\math_numbering_side default
+\quotes_style english
+\dynamic_quotes 0
+\papercolumns 1
+\papersides 2
+\paperpagestyle headings
+\tablestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict true
+\end_header
+
+\begin_body
+
+\begin_layout Standard
+An Englisch document with Japanese parts.
+ Works only with non-TeX fonts or input-encoding set to one of the Japanese
+ (platex) ones.
+ Grüße
+\end_layout
+
+\begin_layout Standard
+
+\lang japanese
+以下の節では\SpecialChar LyX
+でサポートされているRCSコマンドを説明します。それらのコマンドは
+\family sans
+ファイル\SpecialChar menuseparator
+バージョン管理
+\family default
+のサブメニューにあります。\SpecialChar LyX
+は、RCS 
+\lang japanese-cjk
+5.7/5.8に対して試験されています。
+\end_layout
+
+\end_body
+\end_document
diff --git a/autotests/export/latex/es_auto-legacy.lyx b/autotests/export/latex/es_auto-legacy.lyx
new file mode 100644
index 0000000000..0932ce5b9a
--- /dev/null
+++ b/autotests/export/latex/es_auto-legacy.lyx
@@ -0,0 +1,144 @@
+#LyX 2.4 created this file. For more info see https://www.lyx.org/
+\lyxformat 573
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\use_default_options false
+\maintain_unincluded_children false
+\language spanish
+\language_package default
+\inputencoding auto-legacy
+\fontencoding auto
+\font_roman "palatino" "default"
+\font_sans "helvet" "default"
+\font_typewriter "courier" "default"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc true
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\use_microtype false
+\use_dash_ligatures false
+\graphics default
+\default_output_format pdf5
+\output_sync 0
+\bibtex_command default
+\index_command default
+\float_placement class
+\float_alignment class
+\paperfontsize 12
+\spacing single
+\use_hyperref false
+\pdf_title "Introducción a LyX"
+\pdf_author "LyX Team, Spanish translation: Ignacio Garcia"
+\pdf_subject "LyX-documentación Introducción"
+\pdf_keywords "LyX, Documentación"
+\pdf_bookmarks true
+\pdf_bookmarksnumbered true
+\pdf_bookmarksopen true
+\pdf_bookmarksopenlevel 2
+\pdf_breaklinks true
+\pdf_pdfborder false
+\pdf_colorlinks true
+\pdf_backref false
+\pdf_pdfusetitle false
+\pdf_quoted_options "linkcolor=black, citecolor=black, urlcolor=blue, filecolor=blue, pdfpagelayout=OneColumn, pdfnewwindow=true, pdfstartview=XYZ, plainpages=false"
+\papersize a4paper
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 1
+\use_package esint 1
+\use_package mathdots 1
+\use_package mathtools 1
+\use_package mhchem 1
+\use_package stackrel 1
+\use_package stmaryrd 1
+\use_package undertilde 1
+\cite_engine basic
+\cite_engine_type default
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 0
+\use_minted 0
+\index Índice
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 2
+\paragraph_separation indent
+\paragraph_indentation default
+\is_math_indent 0
+\math_numbering_side default
+\quotes_style english
+\dynamic_quotes 0
+\papercolumns 1
+\papersides 1
+\paperpagestyle default
+\tablestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\end_header
+
+\begin_body
+
+\begin_layout Title
+Introducción a \SpecialChar LyX
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset toc
+LatexCommand tableofcontents
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Section
+La filosofía de \SpecialChar LyX
+
+\end_layout
+
+\begin_layout Subsection
+¿What is the problem?
+\end_layout
+
+\begin_layout Standard
+Babel-Spanish uses utf8-encoded auto-strings when detecting Xe/LuaTeX.
+ This leads to wrong output with TeX fonts and legacy 8-bit input encodings,
+ e.g.
+ the ToC-title should be 
+\begin_inset Quotes eld
+\end_inset
+
+Índice
+\begin_inset Quotes erd
+\end_inset
+
+ but is 
+\begin_inset Quotes eld
+\end_inset
+
+Ã ndice
+\begin_inset Quotes erd
+\end_inset
+
+
+\end_layout
+
+\end_body
+\end_document
diff --git a/autotests/export/latex/platex-inputenc-utf8.lyx b/autotests/export/latex/platex-inputenc-utf8.lyx
new file mode 100644
index 0000000000..efa4018d9e
--- /dev/null
+++ b/autotests/export/latex/platex-inputenc-utf8.lyx
@@ -0,0 +1,396 @@
+#LyX 2.4 created this file. For more info see https://www.lyx.org/
+\lyxformat 572
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\begin_preamble
+
+\end_preamble
+\use_default_options true
+\maintain_unincluded_children false
+\language japanese
+\language_package default
+\inputencoding utf8
+\fontencoding auto
+\font_roman "lmodern" "FreeSerif"
+\font_sans "default" "FreeSans"
+\font_typewriter "default" "FreeMono"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc false
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\use_microtype false
+\use_dash_ligatures false
+\graphics default
+\default_output_format pdf
+\output_sync 0
+\bibtex_command default
+\index_command default
+\float_placement class
+\float_alignment class
+\paperfontsize default
+\spacing single
+\use_hyperref false
+\papersize default
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 1
+\use_package esint 1
+\use_package mathdots 1
+\use_package mathtools 1
+\use_package mhchem 1
+\use_package stackrel 1
+\use_package stmaryrd 1
+\use_package undertilde 1
+\cite_engine basic
+\cite_engine_type default
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 1
+\use_minted 0
+\branch na
+\selected 0
+\filename_suffix 0
+\color #faf0e6
+\end_branch
+\branch bisect
+\selected 0
+\filename_suffix 0
+\color #faf0e6
+\end_branch
+\index Index
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 3
+\paragraph_separation indent
+\paragraph_indentation default
+\is_math_indent 0
+\math_numbering_side default
+\quotes_style english
+\dynamic_quotes 0
+\papercolumns 1
+\papersides 1
+\paperpagestyle default
+\tablestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\end_header
+
+\begin_body
+
+\begin_layout Section*
+unicodesymbols and pLaTeX
+\end_layout
+
+\begin_layout Standard
+pLaTeX supports Japanese characters: 日本語（にほんご、にっぽんご[注 1]）は、主に日本国内や日本人同士の間で使用されてい
+る言語である。
+\end_layout
+
+\begin_layout Standard
+Test LyX-supported Unicode characters with pLaTeX.
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/001-4-latin.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/005-7-ipa-modifiers-combining.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/008-greek-and-coptic.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/009-cyrillic.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/009-cyrillic_ru.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/012-hebrew_he.lyx"
+literal "false"
+
+\end_inset
+
+ 
+\end_layout
+
+\begin_layout Plain Layout
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/012-hebrew_he_HE8.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Plain Layout
+Hebrew does not work with XeTeX and TeX-fonts:
+\end_layout
+
+\begin_layout Plain Layout
+Error 256 (driver return code) generating output; file 012-hebrew_he_HE8.pdf
+ may not be valid.
+ 
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset Note Note
+status open
+
+\begin_layout Plain Layout
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/031-thai_th.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Plain Layout
+Thai sets catcodes for characters in Latin-Supplement block leading to wrong
+ output there.
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/065-67-phonetic-extensions.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/068-latin-extended-additional.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/069-greek-extended.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/070-72-general-punctuation-sub-super-currency.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/074-76-letterlike-numberforms-arrows.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/077-mathops.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/078-79-misc-technical-control-pics.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/081-enclosed-alphanumerics.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/082-84-box-drawing-blocks-geometric.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/084-misc-symbols.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/085-dingbats.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/087-90-misc-math-A-arrows-A-B.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/091-92-misc-math-B-supp-math-ops.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/125_152-modifiers-presentation.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+\begin_inset CommandInset include
+LatexCommand input
+filename "unicodesymbols/246-mathematical-alphanumeric.lyx"
+literal "false"
+
+\end_inset
+
+
+\end_layout
+
+\end_body
+\end_document