i18n: add Polish (pl) interface language

Complete Polish catalog (4,492 rows): every menu string, tl! literal,
plural and status/error message, enforced by the existing completeness
tests (complete_menus, KEEPS_MENU_NAMES, COMPLETE_MESSAGES).

- pl.tsv: clean-room translation from the English meaning, following
  common Polish desktop-software conventions (obszar kompozycji for
  artboard, obszar roboczy for workspace, obrys, wypełnienie, próbki…)
- plural_polish: one / few (2–4, not 12–14) / many (0, 5–21, 25…)
- every pl-* locale (pl-PL, pl_PL.UTF-8) resolves to it
- tests: Polish plural forms, vocabulary, nested message translation;
  Polish letters in the bundled-font coverage test
- docs: README, development.md, localization-parity.md

Drafted with AI assistance; native review welcome.

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

crates/ui-egui/src/dialogs/missing_fonts.rs

@@ -739,7 +739,7 @@ mod tests {
         let fr = crate::i18n::Lang::from_code("fr").unwrap();
         let shown = crate::i18n::message(fr, "2 font file(s) are now in /Fonts; 1 couldn't be added: a.otf: larger than 256 MB");
         assert!(shown.contains("se trouvent maintenant dans /Fonts") && shown.contains("a.otf") && shown.contains("plus de 256 Mo"), "{shown}");
-        for code in ["de", "es", "fr", "hu", "it", "ru"] {
+        for code in ["de", "es", "fr", "hu", "it", "pl", "ru"] {
             let lang = crate::i18n::Lang::from_code(code).unwrap();
             for s in [
                 "every search thread stopped on an internal error (please report this bug)",

crates/ui-egui/src/i18n/mod.rs

@@ -81,8 +81,20 @@ fn plural_east_slavic(n: u64) -> usize {
     }
 }
 
+/// Polish: only 1 is `one`; 2–4 (but not 12–14) `few`; everything else (0, 5–21, 25…) `many`
+/// (unlike Russian and Ukrainian, 21, 31 … take `many`: "21 warstw").
+fn plural_polish(n: u64) -> usize {
+    if n == 1 {
+        return 0;
+    }
+    match (n % 10, n % 100) {
+        (2..=4, r) if !(12..=14).contains(&r) => 1,
+        _ => 2,
+    }
+}
+
 /// The registry. English first: it is the fallback and the source language.
-pub static LANGUAGES: [LangInfo; 15] = [
+pub static LANGUAGES: [LangInfo; 16] = [
     LangInfo { code: "en", name: "English", source: "", plural: plural_one_other, complete_menus: false, catalog: OnceLock::new() },
     // Japanese: the whole interface (every menu string and `tl!` literal) and the status and error
     // messages, keeping the product, workspace and perspective preset names in English (`MENU_KEEP_AS_IS`).
@@ -156,6 +168,10 @@ pub static LANGUAGES: [LangInfo; 15] = [
     // English as Spanish; a count takes the singular ("3 réteg"), so plurals have one form. Every
     // `hu-*` locale (including `hu-HU`) resolves here.
     LangInfo { code: "hu", name: "Magyar", source: include_str!("hu.tsv"), plural: plural_none, complete_menus: true, catalog: OnceLock::new() },
+    // Polish: the whole interface and the status and error messages, with one/few/many plurals,
+    // keeping the same names in English as Spanish; every `pl-*` locale (including `pl-PL`)
+    // resolves here.
+    LangInfo { code: "pl", name: "Polski", source: include_str!("pl.tsv"), plural: plural_polish, complete_menus: true, catalog: OnceLock::new() },
     // Brazilian Portuguese: every menu label (`menu_catalogs_translate_every_menu_label`), every
     // `tl!` literal and the plural messages; left English on purpose are the `MENU_KEEP_AS_IS`
     // strings (product name, language names, workspace names, perspective grid presets).

crates/ui-egui/src/i18n/tests.rs

@@ -452,7 +452,7 @@ fn cs() -> Lang {
 }
 
 /// Languages whose catalogs leave [`MENU_KEEP_AS_IS`] in English.
-const KEEPS_MENU_NAMES: [&str; 12] = ["cs", "de", "es", "fr", "hu", "it", "ja", "ko", "pt-br", "ru", "uk", "vi"];
+const KEEPS_MENU_NAMES: [&str; 13] = ["cs", "de", "es", "fr", "hu", "it", "ja", "ko", "pl", "pt-br", "ru", "uk", "vi"];
 
 /// Menu labels the menu-complete catalogs (Czech, German, Spanish, Italian, Japanese, Brazilian Portuguese) show as they are: the product name, a format name, the built-in workspace
 /// names and the perspective grid presets (names, shown untranslated wherever else they appear).
@@ -981,7 +981,7 @@ fn russian_plurals_have_three_forms() {
     assert_eq!(forms, [2, 0, 1, 1, 2, 2, 0, 1, 2, 2, 0]);
 }
 
-/// Czech, German, Spanish, French, Italian and Hungarian letters (and the punctuation their text uses) come from each family's own first font, not
+/// Czech, German, Spanish, French, Italian, Hungarian and Polish letters (and the punctuation their text uses) come from each family's own first font, not
 /// from a fallback further down the stack. (`has_glyph` can't tell: it counts characters of the
 /// face that draws missing glyphs, the first one, as missing.)
 #[test]
@@ -996,7 +996,7 @@ fn latin_script_glyphs_are_available_without_system_fonts() {
             let first = first.unwrap();
             let mut font = fonts.fonts.font(&family);
             let chars = font.characters();
-            for ch in "áčďéěíňóřšťúůýžÁČĎÉĚÍŇÓŘŠŤÚŮÝŽ„“‚‘…–ñÑüÜ¿¡”àèìòùÀÈÌÒÙ«»’âêîôûçëïÿœæÂÊÎÔÛÇËÏŒÆäöÄÖßőűŐŰ\u{a0}".chars()
+            for ch in "áčďéěíňóřšťúůýžÁČĎÉĚÍŇÓŘŠŤÚŮÝŽ„“‚‘…–ñÑüÜ¿¡”àèìòùÀÈÌÒÙ«»’âêîôûçëïÿœæÂÊÎÔÛÇËÏŒÆäöÄÖßőűŐŰąćęłńśźżĄĆĘŁŃŚŹŻ\u{a0}".chars()
             {
                 assert!(chars.get(&ch).is_some_and(|fonts| fonts.contains(&first)), "{first} ({family:?}) has no {ch}");
             }
@@ -1163,7 +1163,7 @@ fn select_key_param_error_is_translated() {
 }
 
 /// Languages whose catalogs cover every status and error message.
-const COMPLETE_MESSAGES: &[&str] = &["cs", "de", "es", "fr", "hu", "it", "ja", "ko", "ru", "uk", "vi"];
+const COMPLETE_MESSAGES: &[&str] = &["cs", "de", "es", "fr", "hu", "it", "ja", "ko", "pl", "ru", "uk", "vi"];
 
 /// Crates whose error and status messages reach the status bar.
 const MESSAGE_CRATES: &[&str] = &["ui-egui", "engine", "doc", "format", "svg", "pdf", "eps", "text", "plugins", "metafile", "cad", "trace"];
@@ -1295,3 +1295,56 @@ fn czech_render_site_follow_up() {
         assert_eq!(trn(cs(), n, "{n} PR", "{n} PRs"), format!("{n} PR"));
     }
 }
+
+fn pl() -> Lang {
+    Lang::from_code("pl").expect("pl registered")
+}
+
+#[test]
+fn polish_plurals_have_three_forms() {
+    let forms: Vec<usize> = [0, 1, 2, 4, 5, 11, 12, 14, 21, 22, 25, 101, 112, 122].into_iter().map(plural_polish).collect();
+    assert_eq!(forms, [2, 0, 1, 1, 2, 2, 2, 2, 2, 1, 2, 2, 2, 1]);
+    // Every Polish plural row has the three forms, and each count picks its own.
+    let (entries, _) = parse_entries(pl().0.source);
+    let mut count = 0;
+    for (ctx, src, tr) in &entries {
+        if ctx != "@plural" {
+            continue;
+        }
+        count += 1;
+        let forms: Vec<&str> = tr.split('|').collect();
+        assert_eq!(forms.len(), 3, "{src}");
+        let (one, other) = src.split_once('|').unwrap();
+        for (n, form) in [(1, 0), (3, 1), (5, 2), (21, 2), (22, 1)] {
+            assert_eq!(trn(pl(), n, one, other), forms[form].replace("{n}", &n.to_string()), "{src}: {n}");
+        }
+    }
+    assert!(count >= 13, "Polish plural rows missing");
+}
+
+/// Polish uses its vector-illustration vocabulary (obszar kompozycji, ścieżka, obrys…), resolves
+/// every `pl-*` locale, counts with one/few/many and translates the reason inside a message too.
+#[test]
+fn polish_reads_as_polish() {
+    for tag in ["pl", "pl-PL", "pl_PL.UTF-8", "PL-pl"] {
+        assert_eq!(lang_from_tag(tag), Some(pl()), "{tag}");
+    }
+    for (en, want) in [
+        ("File", "Plik"),
+        ("Artboard Tool", "Narzędzie Obszar kompozycji"),
+        ("Swatches", "Próbki"),
+        ("Pathfinder", "Odnajdywanie ścieżek"),
+        ("Stroke", "Obrys"),
+        ("Fill", "Wypełnienie"),
+        ("Workspace", "Obszar roboczy"),
+    ] {
+        assert_eq!(tr(pl(), en), want);
+    }
+    for (n, word) in [(1, "warstwa"), (3, "warstwy"), (5, "warstw"), (22, "warstwy"), (21, "warstw")] {
+        assert_eq!(trn(pl(), n, "{n} Layer", "{n} Layers"), format!("{n} {word}"));
+    }
+    assert_eq!(tr_ctx(pl(), "axis", "Both"), "Obie");
+    assert_eq!(tr_id(pl(), "pathfinder.add", "Add"), "Połącz");
+    let nested = "command `object.group` is not available right now: nothing selected";
+    assert_eq!(message(pl(), nested), "polecenie `object.group` jest teraz niedostępne: nic nie zaznaczono");
+}