Qt: Add setup wizard

src/duckstation-qt/qthost.h

@@ -252,6 +252,9 @@ void RunOnUIThread(const std::function<void()>& func, bool block = false);
 /// Returns a list of supported languages and codes (suffixes for translation files).
 std::vector<std::pair<QString, QString>> GetAvailableLanguageList();
 
+/// Default language for the platform.
+const char* GetDefaultLanguage();
+
 /// Call when the language changes.
 void InstallTranslator();