UI: Look up strings in the sections where they're translated

These were looked up in a different section from the one with the translation,
so they always showed in English (the savedata error messages, "Done!" after
moving the memstick, "Switch UMD", "Ask for network permission" and others).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Windows/MainWindowMenu.cpp

@@ -386,8 +386,8 @@ namespace MainWindow {
 	}
 
 	static void UmdSwitchAction(RequesterToken token) {
-		auto mm = GetI18NCategory(I18NCat::MAINMENU);
-		System_BrowseForFile(token, mm->T("Switch UMD"), BrowseFileType::BOOTABLE, [](std::string_view value, int) {
+		auto des = GetI18NCategory(I18NCat::DESKTOPUI);
+		System_BrowseForFile(token, des->T("Switch UMD"), BrowseFileType::BOOTABLE, [](std::string_view value, int) {
 			// This is safe because the callback runs on the emu thread.
 			__UmdReplace(Path(value));
 		});