First commit

frontend/app/composables/useLanguageMenu.ts

@@ -0,0 +1,15 @@
+/* The open state of the reader's language menu, shared like the other popups:
+   the book's Esc handler defers to whatever popup is on top, and the menu
+   steps aside when search or settings opens — popups don't stack in this app. */
+export function useLanguageMenu() {
+  const open = useState<boolean>('language-menu:open', () => false)
+
+  function show() {
+    open.value = true
+  }
+  function hide() {
+    open.value = false
+  }
+
+  return { open, show, hide }
+}