locale: Don't assume 2-letter language codes.

Some languages have 3-letter codes. So instead of splitting the output
of QLocale::name, use QLocale::language and the static
QLocale::languageToString.

src/modules/locale/LocalePage.cpp

@@ -290,7 +290,7 @@ LocalePage::guessLCLocale()
     QStringList linesForLanguage;
     foreach ( QString line, m_localeGenLines )
     {
-        if ( line.startsWith( myLocale.name().left( 2 ) ) )
+        if ( line.startsWith( QLocale::languageToString( myLocale.language() ) ) )
             linesForLanguage.append( line );
     }