For LyX 2.3.0:

Modified:

first step (not German, not Japanese):
- sec. 3.7.3: changed sentences
- sec. 3.9.1: new handling of dashes
- sec. 3.9.2: new section
- sec. 3.9.4.2: section completely rewritten (not French)
- sec. 6.1: new reference format and new options (not French)
- sec. 6.5: section and its subsections completely rewritten
- sec. 6.8: new feature "inverted branches" (not French)
- sec. A.4.3 new menu
- sec. B.12 new sentences (not French)
- sec. C.1.2.3 new sentence (not French)

second step
- sec. 4.6.2: Japanese only: untranslated image captions
- sec. C.2.2.1 new paragraph (not French, not German)

=============
For LyX 2.2.3:

- sec. 2.5.1: (not French) new sentence
- sec. 6.11.4: Japanese only: untranslated note
- sec. 6.10.1: (not French) new footnote
- sec. B.20: (not French) section was renamed

- Shortcuts.lyx: Spanish only: untranslated sentence


For LyX 2.2.1:

- sec. 6.11: new sentence
- sec. B.20: new item


For LyX 2.2.0:

in the first step:
- sec. 3.3.10.1 (Japanese only) changed sentence
- sec. 3.3.10.2 new paragraph about Verbatim*
- sec. 3.4.6: changed paragraph
- sec. 3.7.6: new color names
- sec. 6.7.1: new paragraph
- sec. A.6.10: new sentence
- sec. B.9: (Japanese only) changed sentence
- sec. C.1.2.2: info about compression
- Bibliography: (Japanese only) new entry for the makeindex manpages

in the second step:
- sec. 2.5.2: new section
- sec. 3.4.6: updated description
- sec. 3.9.5: (French and Japanese only) updated menu name
- sec. A.1.13: new formats OpenDocument (Pandoc), OpenDocument (tex4ht) and MS Word Office Open XML
               new reference for Postscript
- sec. A.4.2: new entry
- sec. A.6.2: new paragraph
- sec. A.6.11: new section
- sec. C.2.3: new option
- sec. C.6.1: new dvips option

in the third step:
 the term "longtable" was replaced by "multi-page table"
  please rename all occurrences (including the cross-references and the index
  entries)of longtable accordingly
  occurrences: sec. 4.5.2, A.4.14
- sec. A.2.10: revised
- sec. A.2.11: new subsection
- sec. A.2.12: revised