i18n: add Polish (pl) interface language

Polish menus (every fixed menu entry, 630 rows) and panels (every row of
the Chinese panel catalogs, 695), the undo/redo, Reveal and Assign Shortcut
labels, the macOS Services item, Settings ▸ General ▸ Language and
Match System for pl-* locales. Tests cover the locale mapping, the
settings registry and the macOS application menu.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DukHNvUY45rjRnvtz91x33

crates/engine/src/settings/prefs/choices.rs

@@ -8,6 +8,7 @@ pub const LANGUAGES: &[(&str, &str)] = &[
     ("Deutsch", "de"),
     ("Español", "es"),
     ("Français", "fr"),
+    ("Polski", "pl"),
     ("Português (Brasil)", "pt-br"),
     ("Русский", "ru"),
     ("Українська", "uk"),

crates/engine/src/tests/settings.rs

@@ -1072,6 +1072,14 @@ fn interface_language_is_validated_persisted_and_backward_compatible() {
     cs.load_settings();
     assert_eq!(cs.prefs.general.language, "cs");
     assert_eq!(Prefs::from_json(r#"{"general":{"language":"cs"}}"#).general.language, "cs");
+    // Polish, likewise.
+    assert!(crate::prefs::LANGUAGES.contains(&("Polski", "pl")));
+    s.execute("prefs.set", json!({"key": "general.language", "value": "pl"})).unwrap();
+    assert_eq!(s.execute("prefs.get", json!({"key": "general.language"})).unwrap(), json!("pl"));
+    let mut pl = Session { config: Some(store.clone()), ..Default::default() };
+    pl.load_settings();
+    assert_eq!(pl.prefs.general.language, "pl");
+    assert_eq!(Prefs::from_json(r#"{"general":{"language":"pl"}}"#).general.language, "pl");
     // Georgian too.
     assert!(crate::prefs::LANGUAGES.contains(&("ქართული", "ka")));
     s.execute("prefs.set", json!({"key": "general.language", "value": "ka"})).unwrap();