photocraft/docs/localization.md

UI localisation and live language switching

PhotoCraft uses the same Rust catalog implementation in the native egui shell and the WebAssembly build. English source strings are lookup keys. UTF-8 TSV catalogs supply plain, contextual, command-ID and plural translations; missing entries fall back to English.

Supported languages

Language	Preference code	Integer plural forms
English	en	one / other
简体中文	zh-hans	one form
日本語	ja	one form
한국어	ko	one form
Русский	ru	one / few / many
Українська	uk	one / few / many (teens use many)
Français	fr	singular for 0 and 1 / plural for 2+
繁體中文	zh-hant	one form
Español	es	one / other
Čeština	cs	one / few / other
Deutsch	de	one / other
Bahasa Indonesia	id	one form
Português (Brasil)	pt-br	singular for 0 and 1 / plural for 2+
Italiano	it	one / other
Polski	pl	one / few (2–4, not 12–14) / many
Ελληνικά	el	one / other
Nederlands	nl	one / other

Every non-English catalog covers the current menu labels, tl! literals, blend mode names, and generated preference labels. Tests enforce that coverage. This does not include every engine error or status message: those remain English, as do automation command IDs and user-provided document, layer and preset names.

Switch without restarting

Open Edit > Preferences > Interface > Language and choose a language. The Preferences dialog previews its title, controls and buttons in the chosen language. Cancel discards the preview, Apply commits it without closing the dialog, and OK commits and closes. The rest of the interface follows the committed preference on its next draw. Existing documents, undo history and tools remain available throughout a language change.

The existing preference store saves the selection for future launches. auto follows the native system locale; an unsupported code follows the same fallback. Regional tags such as fr-CA, ko-KR and zh-CN resolve to the corresponding registered catalog. Traditional and Simplified Chinese remain distinct. Every Portuguese locale (pt, pt-BR, pt-PT) uses the Brazilian Portuguese catalog.

First launch and system language

With no saved preference, interface.language defaults to auto, so the first rendered window uses the first supported system UI language. An older preferences file without this field also uses Auto. If detection fails or none of the preferred languages is registered, the UI uses English (en). A saved manual language choice takes precedence on later launches; startup never overwrites it or writes the detected language into the preference file.

The native-only, pinned sys-locale dependency provides safe Rust access to the platform APIs:

• Windows: GetUserPreferredUILanguages, in the user's preferred order. This uses UI languages rather than the Region setting for dates and numbers; they can differ.
• macOS: CFLocaleCopyPreferredLanguages, in preferred order, without starting defaults or depending on a particular .plist representation.
• Linux/BSD: the platform's standard locale environment, including LANGUAGE lists.

PHOTOCRAFT_LOCALE is an optional single-tag override for reproducible launches; an unsupported override falls back to English. Empty overrides use the system. Unix locale variables do not override Windows/macOS UI-language preferences. Tags are read once per process (at most 64, 128 bytes each) and matched against the supported language registry. Changes to the OS language list itself take effect at the next launch. The web build keeps its existing English Auto fallback until browser-locale detection is implemented.

API implementation and licensing: sys-locale.

Agents use the existing prefs.set command through CLI, MCP or the desktop control channel:

{"method":"engine.execute","params":{"command":"prefs.set","params":{"path":"interface.language","value":"ko"}}}

Control requests are processed before synchronising the drawing language, so a request updates the labels in the same rendered frame. Drawing language is local to the UI thread; a scoped preview restores the previous language even if drawing unwinds. Menu and dialog identity continues to use command IDs, independent of translated labels.

This is hot switching among the bundled catalogs. Catalog files are embedded with include_str!; editing a TSV file requires a rebuild. External catalog watching and file-resource hot reload are not implemented.

Fonts

The native lazy CJK font loader prioritises the selected Japanese, Korean or Chinese script. Switching languages rebuilds the font definitions and resets the existing loader, so fonts removed from the definitions can be registered again. Idle frames keep their font cache. Other languages retain the system's CJK fallback preference for document names and text.

Font files are not added to this repository. Native rendering uses installed system fonts and the optional craft-fonts build input; see Fonts. The web build can select every catalog, but CJK glyph delivery and automatic browser-locale detection remain separate outstanding work. Switching catalogs does not supply missing fonts.

Add or maintain a catalog

1. Add <code>.tsv under crates/ui-egui/src/i18n, following the header in ja.tsv.
2. Register its code, native name and plural rule in i18n::LANGUAGES.
3. Translate the meaning of the English source keys. Preserve {name} placeholders, escaped characters and the trailing … on dialog commands. Use @id to disambiguate a command label and @plural for count-sensitive text. Keep product names such as PhotoCraft.
4. Set complete_menus when the catalog covers all enforced keys. Add source and license attribution for translation assets, then run the catalog and shell tests.

cargo test -p photocraft-ui-egui --locked
cargo clippy -p photocraft-ui-egui --all-targets --locked -- -D warnings
cargo xtask i18n-coverage
cargo xtask layers
cargo xtask wasm

Render representative dialogs with the offscreen snapshot example, including a sequence of language changes in one process. Inspect the PNGs for missing glyphs and truncated labels. Translations are original work or reuse the open PhotoCraft contributions credited in ATTRIBUTION.md; no proprietary localisation resources are used.