Add Russian to the language site and the forum placeholderfeature/russian-locale

Russian (ru-RU) is the third locale of the language site: the shell, the
home, overview and getting-started pages, and the page metadata are fully
translated, and the language menu offers it. The documentation sidebar reads
its labels from the page messages instead of a two-way locale test, and the
stored preference is accepted only when it names a supported locale.

The forum placeholder gets the same three languages. Its language control
is now a menu instead of a two-state button, and an unknown stored or
selected value keeps the current language.

The site API lists the new locale. Verified locally: prettier, the frontend
tests, vue-tsc and the Vite build, the backend tests, and a browser run of
the home and overview pages in Russian.

2 files changed, 49 insertions, 6 deletions

diff --git a/frontend/tests/forum.test.mjs b/frontend/tests/forum.test.mjs
index 38771aa..c04df30 100644
--- a/frontend/tests/forum.test.mjs
+++ b/frontend/tests/forum.test.mjs
@@ -18,6 +18,7 @@ function createElement() {
   const attributes = new Map();
   return {
     textContent: "",
+    value: "",
     listeners,
     attributes,
     addEventListener(name, callback) {
@@ -29,6 +30,10 @@ function createElement() {
     click() {
       listeners.get("click")();
     },
+    choose(value) {
+      this.value = value;
+      listeners.get("change")();
+    },
   };
 }
 
@@ -65,7 +70,8 @@ test("forum starts in English and dark mode without offering sign-up", () => {
   const { document, elements } = loadForum();
   assert.equal(document.documentElement.lang, "en");
   assert.equal(document.documentElement.dataset.theme, "dark");
-  assert.equal(elements.get("language").textContent, "DE");
+  assert.equal(elements.get("language").value, "en");
+  assert.equal(elements.get("language").attributes.get("aria-label"), "Language");
   assert.match(elements.get("title").textContent, /isn't open yet/);
   assert.match(elements.get("message").textContent, /no accounts, posts/);
   assert.doesNotMatch(elements.get("message").textContent, /sign up/i);
@@ -73,18 +79,39 @@ test("forum starts in English and dark mode without offering sign-up", () => {
 
 test("forum switches language and keeps the choice", () => {
   const { document, elements, values } = loadForum();
-  elements.get("language").click();
+  elements.get("language").choose("de");
   assert.equal(document.documentElement.lang, "de");
   assert.equal(values.get("vxs-forum-language"), "de");
-  assert.equal(elements.get("language").textContent, "EN");
+  assert.equal(elements.get("language").value, "de");
   assert.match(elements.get("title").textContent, /nicht geöffnet/);
   assert.match(document.title, /Visual X#/);
-  assert.equal(elements.get("language").attributes.get("aria-label"), "Zu Englisch wechseln");
-  elements.get("language").click();
+  assert.equal(elements.get("language").attributes.get("aria-label"), "Sprache");
+  elements.get("language").choose("ru");
+  assert.equal(document.documentElement.lang, "ru");
+  assert.equal(values.get("vxs-forum-language"), "ru");
+  assert.match(elements.get("title").textContent, /Форум пока не открыт/);
+  assert.match(elements.get("message").textContent, /нет ни аккаунтов, ни сообщений/);
+  assert.equal(elements.get("language").attributes.get("aria-label"), "Язык");
+  elements.get("language").choose("en");
   assert.equal(document.documentElement.lang, "en");
   assert.equal(values.get("vxs-forum-language"), "en");
 });
 
+test("forum ignores a language it does not offer", () => {
+  const { document, elements, values } = loadForum({ "vxs-forum-language": "tr" });
+  assert.equal(document.documentElement.lang, "en");
+  elements.get("language").choose("constructor");
+  assert.equal(document.documentElement.lang, "en");
+  assert.equal(elements.get("language").value, "en");
+  assert.equal(values.get("vxs-forum-language"), "tr");
+});
+
+test("forum restores a saved Russian preference", () => {
+  const { document, elements } = loadForum({ "vxs-forum-language": "ru" });
+  assert.equal(document.documentElement.lang, "ru");
+  assert.equal(elements.get("language").value, "ru");
+});
+
 test("forum restores the saved German and light preferences", () => {
   const { document, elements } = loadForum({
     "vxs-forum-language": "de",
@@ -92,7 +119,7 @@ test("forum restores the saved German and light preferences", () => {
   });
   assert.equal(document.documentElement.lang, "de");
   assert.equal(document.documentElement.dataset.theme, "light");
-  assert.equal(elements.get("language").textContent, "EN");
+  assert.equal(elements.get("language").value, "de");
 });
 
 test("forum theme button toggles and persists in both directions", () => {
diff --git a/frontend/tests/seo.test.mjs b/frontend/tests/seo.test.mjs
index c7014b7..45bb6de 100644
--- a/frontend/tests/seo.test.mjs
+++ b/frontend/tests/seo.test.mjs
@@ -75,3 +75,19 @@ test("a missing optional metadata tag does not stop the page title", () => {
   applyPageMetadata("/docs/getting-started", "de-DE");
   assert.equal(globalThis.document.title, "Erste Schritte · Visual X#");
 });
+
+test("the Russian routes have their own titles and keep the canonical URLs", () => {
+  const { document, elements } = fakeDocument();
+  applyPageMetadata("/", "ru-RU");
+  assert.match(document.title, /^Visual X# — Сделать понятной всю программу$/);
+  assert.match(elements.get('meta[name="description"]').content, /нативный язык программирования/);
+  assert.equal(elements.get('link[rel="canonical"]').href, "https://xsharp-lang.xyz/");
+  applyPageMetadata("/docs/overview", "ru-RU");
+  assert.equal(document.title, "Обзор · Visual X#");
+  applyPageMetadata("/docs/getting-started", "ru-RU");
+  assert.equal(document.title, "Начало работы · Visual X#");
+  assert.equal(
+    elements.get('link[rel="canonical"]').href,
+    "https://xsharp-lang.xyz/docs/getting-started",
+  );
+});