i18n: missing translations are reported, never a failure (#2729)

A message a catalog lacks, or translates as an empty string, shows in
English and fails nothing:

- build.rs no longer requires every formats catalog to carry the same
  messages, and tr_format! gets a last arm that formats the English
  source, so a message no catalog has builds.
- Coverage tests (every language translates X) and tests of one
  language's exact wording are gone; the language-switching, layout,
  date, placeholder and user-value tests read the catalog's own value
  instead of a hard-coded translation.
- i18n::tests::translation_gaps_report lists, per language, the plain
  and format messages it lacks and its untranslated What's New lines.
  It always passes; cargo xtask ci
  runs it from the test step's binary after the tests.
- catalogs_load checks that every catalog file is a JSON object of
  strings with each key once; it.json named "Dimensions" twice.

docs/localization-cs.md

@@ -46,8 +46,9 @@ ani anglické zdrojové řetězce. Rozložení panelů a seznamu jazyků je beze
 ## Ověření a revize
 
 Testy `i18n::tests` ověřují registraci příkazu, přepínání přes nabídku a řídicí kanál,
-uložení jazyka, pokrytí katalogů, placeholdery, neutrální formulace počtů, datum, čas
-a české glyfy. Překladové šablony kontroluje také Rust při sestavení.
+uložení jazyka, placeholdery, datum, čas a české glyfy. Překladové šablony kontroluje také
+Rust při sestavení. Chybějící překlady se zobrazují anglicky a vypisuje je
+`i18n::tests::translation_gaps_report`; žádný test kvůli nim neselže.
 
 Při jazykové korektuře doporučujeme zkontrolovat „asistované třídění“, „sada“ pro Stack,
 „bodová barva“, „měkký nátisk“ a názvy kreativních přednastavení.

docs/localization-de.md

@@ -29,8 +29,8 @@ cargo test -p lightcraft-ui-egui i18n::tests
 LIGHTCRAFT_LANGUAGE=de lightcraft-cli snapshot --demo -o deutsch.png --size 1600x1000
 ```
 
-Die Tests prüfen Katalogabdeckung, Platzhalter, Sprachwechsel per Menü und Steuerkanal,
-Speicherung, Datumsformate, unveränderte Benutzernamen und gerenderte Texte sowie Umlaute
-und ß. Ein weiterer Render-Test prüft die Schaltflächenbreiten; der Importtest prüft
+Die Tests prüfen Platzhalter, Sprachwechsel per Menü und Steuerkanal, Speicherung,
+Datumsformate, unveränderte Benutzernamen und gerenderte Texte sowie Umlaute und ß. Fehlende
+Übersetzungen erscheinen auf Englisch; `i18n::tests::translation_gaps_report` listet sie auf. Ein weiterer Render-Test prüft die Schaltflächenbreiten; der Importtest prüft
 auch den Sprachwechsel nach der Hintergrundprüfung der Quellen. Akzeptierte Sprachangaben umfassen `de`, `de-DE`, `de_AT.UTF-8` und `de-CH`;
 gespeichert wird stets `de`. Weitere Hinweise stehen in [localization.md](localization.md).

docs/localization-fi.md

@@ -52,8 +52,9 @@ englanniksi. Käännös ei muuta kirjastotietoja eikä englanninkielisiä lähde
 ## Testaus
 
 `i18n::tests` tarkistaa komennon rekisteröinnin, vaihdon valikosta ja ohjauskanavasta,
-kielen tallennuksen, luetteloiden kattavuuden, paikkamerkit, määrämuodot, päivämäärän, ajan ja
-suomen kirjaimet. Rust tarkistaa muotoilumallit käännösvaiheessa.
+kielen tallennuksen, paikkamerkit, päivämäärän, ajan ja suomen kirjaimet. Rust tarkistaa
+muotoilumallit käännösvaiheessa. Puuttuvat käännökset näkyvät englanniksi, ja
+`i18n::tests::translation_gaps_report` luettelee ne; mikään testi ei epäonnistu niiden takia.
 
 Kielentarkistuksessa kannattaa katsoa erityisesti: ”Väriluokittelu” (Color Grading),
 ”Valoalueet / Valkoiset” (Highlights / Whites), ”Näyttövedos” (Soft Proofing),

docs/localization-ka.md

@@ -19,7 +19,7 @@ not translated. Descriptions for SAM 3 go to the model unchanged.
 ## Georgian script
 
 Mkhedruli has no upper and lower case: `i18n::upper_first` leaves Georgian letters alone, and the
-interface never uses Mtavruli (a test checks the whole catalog). Commands are verbal nouns. Counts
+interface never uses Mtavruli. Commands are verbal nouns. Counts
 are count-neutral, noun first (`იმპორტირებულია ფოტო: 3`); English plural endings are dropped with
 `{:.0}`. Dates read `კვირა, 20.09.2026` (`{weekday}, {day:02}.{month:02}.{year}`), months `09.2026`.
 
@@ -73,7 +73,7 @@ cargo test -p lightcraft-ui-egui i18n::tests -- --nocapture
 LIGHTCRAFT_LANGUAGE=ka lightcraft-cli snapshot --demo -o georgian.png --size 1600x1000
 ```
 
-The tests check catalog coverage, placeholders, switching language by menu and control channel,
-saving, the `ka` locale tags, dates, count wording, the absence of Mtavruli and that sentence case
-keeps Georgian lowercase. More notes are in
+The tests check placeholders, switching language by menu and control channel, saving, the `ka`
+locale tags, dates and that sentence case keeps Georgian lowercase. Messages Georgian lacks show in
+English; `i18n::tests::translation_gaps_report` lists them. More notes are in
 [localization.md](localization.md).

docs/localization-vi.md

@@ -66,8 +66,9 @@ LIGHTCRAFT_LANGUAGE=vi lightcraft-cli snapshot --demo -o vi.png --size 1600x1000
 LIGHTCRAFT_LANGUAGE=vi lightcraft-cli snapshot --demo -o vi-narrow.png --size 1280x800
 ```
 
-Các test tiếng Việt bắt buộc phủ catalog union, nhãn lệnh/control/Settings/Smart Album,
-đổi ngôn ngữ, lưu `vi`, formats, ngày, dữ liệu người dùng, và glyph dấu.
+Các test tiếng Việt kiểm tra đổi ngôn ngữ, lưu `vi`, formats, ngày, dữ liệu người dùng và glyph
+dấu. Chuỗi còn thiếu hiện bằng tiếng Anh và được `i18n::tests::translation_gaps_report` liệt kê;
+không test nào thất bại vì thiếu bản dịch.
 
 ## Nguồn dịch (clean-room)
 

docs/localization-zh-hans.md

@@ -34,5 +34,6 @@ LightCraft 的界面支持英语、简体中文、繁体中文（台湾）和日
 
 `LIGHTCRAFT_LANGUAGE=zh-hans lightcraft-cli snapshot ...` 可以渲染中文界面用于检查。
 
-翻译是否完整、两种目录的键与占位符是否一致、字形是否齐全，都由
+两种目录的占位符是否一致、字形是否齐全，由
 `cargo test -p lightcraft-ui-egui i18n::tests` 验证（字形检查只在指定 `CRAFT_FONTS_DIR` 时实际执行）。
+缺少的译文显示为英文，由 `i18n::tests::translation_gaps_report` 列出，不会让测试失败。

docs/localization.md

@@ -12,11 +12,10 @@ are in [`localization-zh-hans.md`](localization-zh-hans.md), [`localization-zh-h
 
 1. **Translate the two catalogs.** Copy `locales/ja.json` and `locales/ja-formats.json` to
    `locales/<code>.json` and `locales/<code>-formats.json`, then translate the values. Keys are the
-   English source strings and must stay byte-for-byte identical. The plain catalog may grow at its
-   own pace: a message it lacks shows in English, and `cargo test -p lightcraft-ui-egui i18n::tests
-   -- --nocapture` lists the gaps (it fails on an empty entry or mismatched placeholders). The
-   formats catalog must carry every message (the build fails otherwise; a message copied in English,
-   value equal to its key, is an untranslated placeholder until someone translates it), including the date
+   English source strings and must stay byte-for-byte identical. Both catalogs may grow at their
+   own pace: a message a catalog lacks, or translates as an empty string, shows in English, and
+   nothing fails. The translation gaps report lists what each language lacks (see
+   [Testing and looking at it](#testing-and-looking-at-it)). The formats catalog also holds the date
    patterns (`{year}`, `{month} {year}`, `{weekday}, {day} {month} {year}`…) that date headings and
    capture times use in every language but English; weekday names go in the plain catalog.
 2. **Add the table entry** in `crates/ui-egui/src/i18n.rs`:
@@ -81,18 +80,23 @@ tr_format!("Added {n} photo{} to “{}”", if n == 1 { "" } else { "s" }, album
   `"已将 {n} 张照片添加到“{1}”{0:.0}"`. Keep the source's spec (`{:.1}`, `{d:+}`, `{:.0}%`).
 - `format!` rejects an unused argument, so a value a language does not need — the English plural
   suffix (`"s"` / `""`) — is consumed as `{:.0}` (a string at precision 0 prints nothing).
-- Every formats catalog carries the same messages (`build.rs` fails the build otherwise), and a
-  `tr_format!` call whose message is in no catalog does not compile: add it to every
-  `*-formats.json` file.
+- A language whose formats catalog lacks a message shows the English source there, and a
+  `tr_format!` call whose message is in no catalog formats the English source (the macro's last
+  arm). A new message builds with no catalog entry.
 
 ## Testing and looking at it
 
 ```sh
-cargo test -p lightcraft-ui-egui i18n::tests                       # catalogs, keys, placeholders, commands
+cargo test -p lightcraft-ui-egui i18n::tests                       # catalogs load, placeholders, switching
 CRAFT_FONTS_DIR=../craft-fonts cargo test -p lightcraft-ui-egui i18n::tests   # + glyph coverage
+cargo test -p lightcraft-ui-egui --lib -- --exact i18n::tests::translation_gaps_report --nocapture
 ```
 
-The glyph tests are skipped without `CRAFT_FONTS_DIR` (there are no CJK faces to check then).
+The tests fail on a broken catalog (malformed JSON, a repeated key, placeholders that differ from
+the source), never on a missing translation. The last command is the translation gaps report: per
+language, the count and list of plain and format messages it lacks and the number of untranslated
+What's New lines. It always passes, and `cargo xtask ci` prints it after its test step. The glyph
+tests are skipped without `CRAFT_FONTS_DIR` (there are no CJK faces to check then).
 To look at a language, render it headless:
 
 ```sh
@@ -114,5 +118,5 @@ when a region has no dedicated entry.
 Help ▸ What's New shows `docs/whats-new.md`, and each of its lines (a heading, or one wrapped line of a
 bullet, without the `- ` or `### `) is looked up like any message, so a catalog can translate the notes
 line by line (German does). A line that is re-wrapped or edited no longer matches its translation and
-shows in English until the catalog is updated; untranslated lines are reported by
-`display_label_gaps_are_reported`, never failed.
+shows in English until the catalog is updated; the translation gaps report counts the untranslated
+lines.