Merge branch 'translation-lookup-fixes' of https://github.com/vslavik/wxWidgets

Restore correct translation language lookup taking into account message
IDs language correctly when it is present in the preferred UI languages
but is not the first language in them and other similar corner cases.

Also add unit tests verifying that this code logic, already changed many
times in the past, does behave correctly now.

See #24297.

interface/wx/translation.h

@@ -85,6 +85,11 @@ public:
         translations offered to the user. To do this, pass the app's main
         catalog as @a domain.
 
+        @note
+        The returned list does not include messages ID language, i.e. the
+        language (typically English) included in the source code. In the use
+        case described above, that language needs to be added manually.
+
         @see GetBestTranslation()
      */
     wxArrayString GetAvailableTranslations(const wxString& domain) const;
@@ -97,6 +102,12 @@ public:
         it simply returns the language set with SetLanguage() if it's available
         or empty string otherwise.
 
+        @warning
+        This function does not consider messages ID language (typically
+        English) and can return inappropriate language if it is anywhere in
+        user's preferred languages list. Use GetBestTranslation() instead
+        unless you have very specific needs.
+
         @since 3.3.0
      */
     wxString GetBestAvailableTranslation(const wxString& domain);
@@ -158,6 +169,16 @@ public:
         All loaded catalogs will be used for message lookup by GetString() for
         the current locale.
 
+        @param domain
+            The catalog domain to add.
+
+        @param msgIdLanguage
+            Specifies the language of "msgid" strings in source code
+            (i.e. arguments to GetString(), wxGetTranslation() and the _() macro).
+            It is used if AddCatalog() cannot find any catalog for current language:
+            if the language is same as source code language, then strings from source
+            code are used instead.
+
         @return
             @true if catalog was successfully loaded, @false otherwise, usually
             because it wasn't found. Note that unlike AddCatalog() this
@@ -167,9 +188,10 @@ public:
             selected or system-default languages, but is not necessarily an
             error if no translations are needed in the first place.
 
-        @since 3.3.0
+        @since 3.2.5
      */
-    bool AddAvailableCatalog(const wxString& domain);
+    bool AddAvailableCatalog(const wxString& domain,
+                             wxLanguage msgIdLanguage = wxLANGUAGE_ENGLISH_US);
 
     /**
         Add a catalog for use with the current locale or fall back to the