feat: add URL-based language switching (#de, #pl, #es, #ar, #uk)

- Visit #de to switch to German and go to home
- Visit #pl for Polish, #es for Spanish, #ar for Arabic, #uk for Ukrainian
- Language is persisted to localStorage
- URL is cleaned up after switching (hash removed)

src/app.js

@@ -1937,6 +1937,13 @@ function handleRoute(shouldUpdateUrl = true) {
 		case RouteType.LESSON:
 			navigateToLesson(route.moduleId, route.lessonIndex, shouldUpdateUrl);
 			break;
+		case RouteType.LANGUAGE:
+			// Switch language and redirect to home
+			setLanguage(route.lang);
+			applyTranslations();
+			history.replaceState(null, "", window.location.pathname);
+			showLandingPage();
+			return; // Skip updateNavHighlight/updatePageMeta since we're redirecting
 		default:
 			showLandingPage();
 	}

src/helpers/router.js

@@ -4,6 +4,7 @@
  *
  * Route formats:
  * - #              -> Home landing page
+ * - #de, #pl, #ar  -> Switch language and go to home
  * - #css           -> CSS section landing
  * - #html          -> HTML section landing
  * - #tailwind      -> Tailwind section landing
@@ -18,7 +19,8 @@ export const RouteType = {
 	HOME: "home",
 	SECTION: "section",
 	REFERENCE: "reference",
-	LESSON: "lesson"
+	LESSON: "lesson",
+	LANGUAGE: "language"
 };
 
 /**
@@ -26,6 +28,11 @@ export const RouteType = {
  */
 const SECTIONS = ["css", "html", "tailwind"];
 
+/**
+ * Valid language codes for URL-based switching
+ */
+const LANGUAGES = ["en", "de", "pl", "es", "ar", "uk"];
+
 /**
  * Parse current URL hash into route info
  * @returns {{ type: string, moduleId?: string, lessonIndex?: number, sectionId?: string, refId?: string } | null}
@@ -44,6 +51,11 @@ export function parseHash() {
 	if (parts.length === 1) {
 		const segment = parts[0];
 
+		// Language switching (e.g., #de, #pl, #ar)
+		if (LANGUAGES.includes(segment)) {
+			return { type: RouteType.LANGUAGE, lang: segment };
+		}
+
 		// Section landing pages
 		if (SECTIONS.includes(segment)) {
 			return { type: RouteType.SECTION, sectionId: segment };