Recognize "ll_LL" as at language "ll" in GetSystemLanguage()

If we can't find an exact match for the system locale in the database,
try to at least find the corresponding language.

This is almost certainly what the intention of the original code was, as
otherwise the entire loop was useless because it couldn't find anything
that wouldn't have been found in the loop just above.

This allows to correctly load German translations when using unsupported
locale such as "de_IT", for example.

See #19082.

src/common/intl.cpp

@@ -732,7 +732,7 @@ inline bool wxGetNonEmptyEnvVar(const wxString& name, wxString* value)
     {
         for ( i = 0; i < count; i++ )
         {
-            if ( ms_languagesDB->Item(i).CanonicalName == lang )
+            if ( ExtractLang(ms_languagesDB->Item(i).CanonicalName) == lang )
             {
                 break;
             }