Revise how the language system works.

On Win32, the Language menubar is eliminated in favour of displaying a NewLanguageScreen on screens that are of type UIDialogScreenWithBackground/UIScreenWithBackground; UIScreen inheriting screens (e.g. GamePauseScreen) still require manual additions.

UI/MainScreen.cpp

@@ -650,20 +650,11 @@ UI::EventReturn MainScreen::OnGameSelectedInstant(UI::EventParams &e) {
 UI::EventReturn MainScreen::OnGameSettings(UI::EventParams &e) {
 	// screenManager()->push(new SettingsScreen());
 	auto gameSettings = new GameSettingsScreen("", "");
-	gameSettings->OnLanguageChanged.Handle(this, &MainScreen::OnLanguageChange);
 	gameSettings->OnRecentChanged.Handle(this, &MainScreen::OnRecentChange);
 	screenManager()->push(gameSettings);
 	return UI::EVENT_DONE;
 }
 
-UI::EventReturn MainScreen::OnLanguageChange(UI::EventParams &e) {
-	RecreateViews();
-	if (host) {
-		host->UpdateUI();
-	}
-	return UI::EVENT_DONE;
-}
-
 UI::EventReturn MainScreen::OnRecentChange(UI::EventParams &e) {
 	RecreateViews();
 	if (host) {
@@ -852,10 +843,22 @@ UI::EventReturn GamePauseScreen::OnCwCheat(UI::EventParams &e) {
 	return UI::EVENT_DONE;
 }
 
+UI::EventReturn GamePauseScreen::OnLanguageChange(UI::EventParams &e) {
+	RecreateViews();
+	if (host) {
+		host->UpdateUI();
+	}
+
+	return UI::EVENT_DONE;
+}
+
 void GamePauseScreen::sendMessage(const char *message, const char *value) {
 	// Since the language message isn't allowed to be in native, we have to have add this
 	// to every screen which directly inherits from UIScreen(which are few right now, luckily).
-	if (!strcmp(message, "language")) {
-		screenManager()->RecreateAllViews();
+	I18NCategory *de = GetI18NCategory("Developer");
+	if (!strcmp(message, "language screen")) {
+		auto langScreen = new NewLanguageScreen(de->T("Language"));
+		langScreen->OnChoice.Handle(this, &GamePauseScreen::OnLanguageChange);
+		screenManager()->push(langScreen);
 	}
 }