Texts and languages

The app speaks English and Russian. Every word on screen comes from one catalog; nothing is fetched from the internet.

Where the words are

What	Where
Interface texts	`src/shared/i18n/catalog.ts`: two objects, `en` and `ru`, with the same keys. Read with i18next and react-i18next (`src/renderer/i18n.ts`); main uses `createTranslator` from `src/shared/i18n/index.ts` for dialogs it shows itself.
Lesson texts	`src/shared/lessons/texts.en.ts`, `texts.ru.ts`.
Built-in knowledge	`src/shared/knowledge/coreKnowledge.en.ts`, `coreKnowledge.ru.ts`.
Errors from main	Main sends fixed English sentences; `ERROR_KEYS` in `src/shared/i18n/index.ts` maps each to a catalog key.
Help	`docs/wiki/`: `Page.md` in English, `Page.ru.md` in Russian. Writing wiki pages
Release notes	`docs/releases/vX.Y.Z.md` and `vX.Y.Z.ru.md`.

Write the sentence a person needs, in plain words, with the action named as the menu names it.
A value goes in through {{name}}, never glued on in a component. Numbers through {{count, number}}.
Plurals use the i18next suffixes _one, _few, _many and _other; both languages carry all four keys.
A key, a password or a token never goes into a text.
What the person wrote, workflow JSON, node class names, port types, model names and file names stay as they are, in any language.

A new profile starts in Russian (nonSecretDefaults.language = 'ru' in src/shared/config/schema.ts). The person switches in Settings ▸ Appearance & Motion ▸ Language; the window changes at once, Save keeps it.
The assistant answers in the interface language unless Settings ▸ Assistant ▸ Answer language says otherwise.
File dialogs use the saved language.

tests/unit/locale.test.ts: both languages have the same keys; plurals and number grouping work; errors are redacted.
tests/unit/i18nUsage.test.ts: every place that fills a template gives it all its values, so {{done}} never reaches the screen.
tests/e2e/locale.test.ts: the window in both languages, with no foreign word or raw key on any tab.
The layout walk (Testing) goes through every screen in both languages.

Add the language code to AppLanguage and to the language enum in src/shared/config/schema.ts, with a migration if the stored value needs one (The database and migrations).
Add a third object to catalog.ts with every key; locale.test.ts lists what is missing.
Add lesson texts and built-in knowledge in that language (LessonLanguage, KNOWLEDGE_LANGUAGES).
Add the option to the Language setting, and the language to the Help reader (HelpLanguage in src/shared/contracts/about.ts, scripts/build-assets.js).
Add Page.<code>.md for every wiki page and extend tests/unit/wiki.test.ts.
Run the layout walk in the new language: longer words find every place where a text does not fit.