Improve list of available languages for UI l10n.

Add a new tag HasGuiSupport to language file. Add it for all l10ns
that we currently ship. The po files that are unused are not currently
tagged as available, but this could be done, since the code later
checks that the translation is actually there.

This new information is used in GuiPrefs when populating the language
combox.

The new scheme implies that adding a new language is now a two-step
process:
* the language code has to be added to po/LINGUAS, as before;
* one of the entries of the lib/language file has to be selected as
  reference and be given the "HasGuiSupport true" property.

README.localization

@@ -94,9 +94,10 @@ In order to test your translation you need to obtain the LyX sources
 (from the git repository) and replace the existing .po with yours.
 Afterwards, you should compile and optionally install LyX (check the
 INSTALL file for your OS). Note that, as of LyX 2.1, it is not
-necessary anymore to install anything. In order to run LyX with your
+necessary anymore to install anything.
-translation, change the current language in Preferences dialog or use
+
-the appropriate LANG variable:
+In order to run LyX with your translation, change the current language
+in Preferences dialog or use the appropriate LANG variable:
 
   On Linux: LANG=xx_CC lyx
   On Windows, you need to change the lyx.bat file and write: set LANG=xx_CC
@@ -104,6 +105,12 @@ the appropriate LANG variable:
 xx stands for your language code. CC stands for your country code. So to get,
 e.g., Czech, the code is "cs_CZ".
 
+Another possibility is to use the Preferences dialog to set LyX UI to
+use your language. Note that, as of LyX 2.2, a newly introduced
+language will not appear in the languages combox unless it corresponds
+to an entry of the lib/languages file that has a "HasGuiSupport true"
+property. See this file for more details.
+
 The most comfortable way to see your updated translation while
 editing, is running (in linux) "make xx.gmo" in the po directory to
 compile updated xx.po translation and then run LyX.

lib/languages

@@ -6,6 +6,7 @@
 #
 # Language <lyxname>
 #	GuiName            "<Gui Name>"
+#	HasGuiSupport      <true|false>
 #	BabelName          <babelname>
 #	PolyglossiaName    <polyglossianame>
 #	PolyglossiaOpts    "<language-specific options>"
@@ -31,6 +32,13 @@
 #
 # * Omitted elements will be treated as empty (if string) or "false"
 #   (if boolean).
+# * When HasGuiSupport is true, the language is candidate to appear in
+#   the list of possible GUI languages in the Preferences dialog. It
+#   will actually appear there only if a corresponding .mo file can be
+#   found among the translations. When several languages correspond to
+#   the same translation -- like English, English (US) and English
+#   (UK) -- try to select the entry that is most generic -- here
+#   English.
 # * The QuoteStyle arguments correspond to the following styles:
 #   - danish:  >>text<<  >text<   (inward guillemets)
 #   - english: ``text''  `text'   (66_99)
@@ -141,6 +149,7 @@ End
 # to switch the language the way of the ArabTeX-package
 Language arabic_arabtex
 	GuiName          "Arabic (ArabTeX)"
+	HasGuiSupport    true
 	BabelName        arabtex
 	QuoteStyle       french
 	Encoding         cp1256
@@ -206,6 +215,7 @@ End
 
 Language bahasa
 	GuiName          "Indonesian"
+	HasGuiSupport    true
 	BabelName        bahasa
 	PolyglossiaName  bahasai
 	QuoteStyle       english
@@ -224,6 +234,7 @@ End
 
 Language basque
 	GuiName          "Basque"
+	HasGuiSupport    true
 	BabelName        basque
 	PolyglossiaName  basque
 	QuoteStyle       french
@@ -246,6 +257,7 @@ End
 
 Language brazilian
 	GuiName          "Portuguese (Brazil)"
+	HasGuiSupport    true
 	BabelName        brazil
 	PolyglossiaName  brazil
 	QuoteStyle       english
@@ -305,6 +317,7 @@ End
 
 Language catalan
 	GuiName          "Catalan"
+	HasGuiSupport    true
 	BabelName        catalan
 	PolyglossiaName  catalan
 	PolyglossiaOpts  "babelshorthands=true"
@@ -316,6 +329,7 @@ End
 # uses CJK package
 Language chinese-simplified
 	GuiName          "Chinese (simplified)"
+	HasGuiSupport    true
 	Encoding         euc-cn
 	QuoteStyle       english
 	LangCode         zh_CN
@@ -325,6 +339,7 @@ End
 # uses CJK package
 Language chinese-traditional
 	GuiName         "Chinese (traditional)"
+	HasGuiSupport    true
 	QuoteStyle       english
 	Encoding        utf8-cjk
 	LangCode        zh_TW
@@ -350,6 +365,7 @@ End
 
 Language czech
 	GuiName          "Czech"
+	HasGuiSupport    true
 	BabelName        czech
 	PolyglossiaName  czech
 	QuoteStyle       german
@@ -359,6 +375,7 @@ End
 
 Language danish
 	GuiName          "Danish"
+	HasGuiSupport    true
 	BabelName        danish
 	PolyglossiaName  danish
 	QuoteStyle       danish
@@ -376,6 +393,7 @@ End
 
 Language dutch
 	GuiName          "Dutch"
+	HasGuiSupport    true
 	BabelName        dutch
 	PolyglossiaName  dutch
 	PolyglossiaOpts  "babelshorthands=true"
@@ -386,6 +404,7 @@ End
 
 Language english
 	GuiName          "English"
+	HasGuiSupport    true
 	BabelName        english
 	PolyglossiaName  english
 	QuoteStyle       english
@@ -434,6 +453,7 @@ End
 
 Language finnish
 	GuiName          "Finnish"
+	HasGuiSupport    true
 	BabelName        finnish
 	PolyglossiaName  finnish
 	QuoteStyle       swedish
@@ -444,6 +464,7 @@ End
 # We redefine \og and \fg (guillemets) for older french language definitions
 Language french
 	GuiName          "French"
+	HasGuiSupport    true
 	BabelName        french
 	PolyglossiaName  french
 	QuoteStyle       french
@@ -459,6 +480,7 @@ End
 
 Language galician
 	GuiName          "Galician"
+	HasGuiSupport    true
 	BabelName        galician
 	PolyglossiaName  galician
 	QuoteStyle       french
@@ -493,6 +515,7 @@ End
 
 Language ngerman
 	GuiName          "German"
+	HasGuiSupport    true
 	BabelName        ngerman
 	PolyglossiaName  german
 	PolyglossiaOpts  "babelshorthands=true"
@@ -532,6 +555,7 @@ End
 
 Language greek
 	GuiName           "Greek"
+	HasGuiSupport     true
 	BabelName         greek
 	PolyglossiaName   greek
 	QuoteStyle        french
@@ -555,6 +579,7 @@ End
 
 Language hebrew
 	GuiName           "Hebrew"
+	HasGuiSupport     true
 	BabelName         hebrew
 	PolyglossiaName   hebrew
 	Encoding          cp1255
@@ -599,6 +624,7 @@ End
 # language. We therefore the name of its hunspell dictionary.
 Language interlingua
 	GuiName          "Interlingua"
+	HasGuiSupport    true
 	BabelName        interlingua
 	PolyglossiaName  interlingua
 	Encoding         iso8859-15
@@ -616,6 +642,7 @@ End
 
 Language italian
 	GuiName          "Italian"
+	HasGuiSupport    true
 	BabelName        italian
 	PolyglossiaName  italian
 	QuoteStyle       french
@@ -630,6 +657,7 @@ End
 # InternalEncoding to true.
 Language japanese
 	GuiName          "Japanese"
+	HasGuiSupport    true
 	BabelName        japanese
 	Encoding         jis-platex
 	LangCode         ja_JP
@@ -729,6 +757,7 @@ End
 
 Language magyar
 	GuiName          "Hungarian"
+	HasGuiSupport    true
 	BabelName        magyar
 	PolyglossiaName  magyar
 	QuoteStyle       polish
@@ -767,6 +796,7 @@ End
 
 Language norsk
 	GuiName          "Norwegian (Bokmaal)"
+	HasGuiSupport    true
 	BabelName        norsk
 	PolyglossiaName  norsk
 	QuoteStyle       french
@@ -776,6 +806,7 @@ End
 
 Language nynorsk
 	GuiName          "Norwegian (Nynorsk)"
+	HasGuiSupport    true
 	BabelName        nynorsk
 	PolyglossiaName  nynorsk
 	QuoteStyle       french
@@ -804,6 +835,7 @@ End
 
 Language polish
 	GuiName          "Polish"
+	HasGuiSupport    true
 	BabelName        polish
 	PolyglossiaName  polish
 	QuoteStyle       polish
@@ -813,6 +845,7 @@ End
 
 Language portuguese
 	GuiName          "Portuguese"
+	HasGuiSupport    true
 	BabelName        portuges
 	PolyglossiaName  portuges
 	QuoteStyle       english
@@ -822,6 +855,7 @@ End
 
 Language romanian
 	GuiName          "Romanian"
+	HasGuiSupport    true
 	BabelName        romanian
 	PolyglossiaName  romanian
 	QuoteStyle       polish
@@ -831,6 +865,7 @@ End
 
 Language russian
 	GuiName          "Russian"
+	HasGuiSupport    true
 	BabelName        russian
 	PolyglossiaName  russian
 	QuoteStyle       french
@@ -867,6 +902,7 @@ End
 
 Language serbian
 	GuiName          "Serbian"
+	HasGuiSupport    true
 	BabelName        serbianc
 	PolyglossiaName  serbian
 	QuoteStyle       german
@@ -887,6 +923,7 @@ End
 
 Language slovak
 	GuiName          "Slovak"
+	HasGuiSupport    true
 	BabelName        slovak
 	PolyglossiaName  slovak
 	QuoteStyle       german
@@ -905,6 +942,7 @@ End
 
 Language spanish
 	GuiName          "Spanish"
+	HasGuiSupport    true
 	BabelName        spanish
 	PolyglossiaName  spanish
 	QuoteStyle       french
@@ -930,6 +968,7 @@ End
 
 Language swedish
 	GuiName          "Swedish"
+	HasGuiSupport    true
 	BabelName        swedish
 	PolyglossiaName  swedish
 	QuoteStyle       swedish
@@ -984,6 +1023,7 @@ End
 
 Language turkish
 	GuiName          "Turkish"
+	HasGuiSupport    true
 	BabelName        turkish
 	PolyglossiaName  turkish
 	QuoteStyle       french
@@ -1008,6 +1048,7 @@ End
 
 Language ukrainian
 	GuiName          "Ukrainian"
+	HasGuiSupport    true
 	BabelName        ukrainian
 	PolyglossiaName  ukrainian
 	QuoteStyle       french

src/Language.cpp

@@ -74,6 +74,7 @@ bool Language::readLanguage(Lexer & lex)
 		LA_END,
 		LA_FONTENC,
 		LA_GUINAME,
+		LA_HAS_GUI_SUPPORT,
 		LA_INTERNAL_ENC,
 		LA_LANG_CODE,
 		LA_LANG_VARIETY,
@@ -94,6 +95,7 @@ bool Language::readLanguage(Lexer & lex)
 		{ "end",                  LA_END },
 		{ "fontencoding",         LA_FONTENC },
 		{ "guiname",              LA_GUINAME },
+		{ "hasguisupport",        LA_HAS_GUI_SUPPORT },
 		{ "internalencoding",     LA_INTERNAL_ENC },
 		{ "langcode",             LA_LANG_CODE },
 		{ "langvariety",          LA_LANG_VARIETY },
@@ -153,6 +155,9 @@ bool Language::readLanguage(Lexer & lex)
 		case LA_GUINAME:
 			lex >> display_;
 			break;
+		case LA_HAS_GUI_SUPPORT:
+			lex >> has_gui_support_;
+			break;
 		case LA_INTERNAL_ENC:
 			lex >> internal_enc_;
 			break;

src/Language.h

@@ -33,7 +33,7 @@ class Language {
 public:
 	///
 	Language() : rightToLeft_(false), encoding_(0), internal_enc_(false),
-				 as_babel_options_(false) {}
+				 as_babel_options_(false), has_gui_support_(false) {}
 	/// LyX language name
 	std::string const lang() const { return lang_; }
 	/// Babel language name
@@ -81,6 +81,8 @@ public:
 	std::string const fontenc() const { return fontenc_; }
 	/// This language needs to be passed to babel itself (not the class)
 	bool asBabelOptions() const { return as_babel_options_; }
+	/// This language correspongs to a translation of the GUI
+	bool hasGuiSupport() const { return has_gui_support_; }
 	///
 	bool read(Lexer & lex);
 	///
@@ -127,6 +129,8 @@ private:
 	///
 	bool as_babel_options_;
 	///
+	bool has_gui_support_;
+	///
 	TranslationMap layoutTranslations_;
 };
 
@@ -158,7 +162,6 @@ public:
 	const_iterator begin() const { return languagelist.begin(); }
 	///
 	const_iterator end() const { return languagelist.end(); }
-	///
 
 private:
 	///

src/frontends/qt4/GuiPrefs.cpp

@@ -2309,19 +2309,16 @@ PrefLanguage::PrefLanguage(GuiPreferences * form)
 	startCommandED->setValidator(new NoNewLineValidator(startCommandED));
 	endCommandED->setValidator(new NoNewLineValidator(endCommandED));
 
-	uiLanguageCO->clear();
-
-	QAbstractItemModel * language_model = guiApp->languageModel();
-	// FIXME: it would be nice if sorting was enabled/disabled via a checkbox.
-	language_model->sort(0);
 	defaultDecimalPointLE->setInputMask("X; ");
 	defaultDecimalPointLE->setMaxLength(1);
 
 	defaultLengthUnitCO->addItem(lyx::qt_(unit_name_gui[Length::CM]), Length::CM);
 	defaultLengthUnitCO->addItem(lyx::qt_(unit_name_gui[Length::IN]), Length::IN);
 
-	set<string> added;
+	QAbstractItemModel * language_model = guiApp->languageModel();
+	language_model->sort(0);
 	uiLanguageCO->blockSignals(true);
+	uiLanguageCO->clear();
 	uiLanguageCO->addItem(qt_("Default"), toqstr("auto"));
 	for (int i = 0; i != language_model->rowCount(); ++i) {
 		QModelIndex index = language_model->index(i, 0);
@@ -2335,9 +2332,8 @@ PrefLanguage::PrefLanguage(GuiPreferences * form)
 		if (name != form->rc().gui_language
 		    && name != lyxrc.gui_language
 		    && (!Messages::available(lang->code())
-			|| added.find(lang->code()) != added.end()))
+		        || !lang->hasGuiSupport()))
 			continue;
-		added.insert(lang->code());
 		uiLanguageCO->addItem(index.data(Qt::DisplayRole).toString(),
 		                      index.data(Qt::UserRole).toString());
 	}