add(ui/ux): german and english ui with a toggle in the navbar

README.md

@@ -26,6 +26,9 @@ the same mount, otherwise moving turns into copy + delete.
 | `WORDARR_HARDCOVER_TOKEN` | – | Hardcover API token, the best ebook source; without it Hardcover is skipped |
 | `WORDARR_GOOGLE_BOOKS_KEY` | – | optional, only needed when the keyless Google Books quota runs dry |
 
+The UI speaks German and English; the button next to the navigation switches
+between them and remembers the choice. Without one, the browser language decides.
+
 ## Usage
 
 1. **Libraries** – create one per target folder with a media type, a naming