docs: publish translated docs in twelve languages and the tool that maintains them (#3280)

CONTRIBUTING.md

@@ -126,6 +126,10 @@ pre-commit run --all-files
 - Add type hints to all functions
 - Include docstrings for public APIs
 
+## Documentation and Translations
+
+Documentation contributions are English only: the pages under `docs/` are the source of truth, and the translated documentation sites are generated from them, guided by the per-language style guides and glossaries under `i18n/<lang>/`. Never edit the generated pages under `i18n/<lang>/pages/`—the tool can't tell a hand edit from its own output, so the edit persists unchecked, is carried forward into future runs, and hides the real fix. To fix a translation, change that language's `instructions.md` or `glossary.json` (or the English page, if that's where the problem is) and re-run `translate --lang <code> --pages <page> …` for the affected pages; the fix then carries into every future run. See [`i18n/README.md`](i18n/README.md) for the details.
+
 ## Pull Requests
 
 By the time you open a PR, the "what" and "why" should already be settled in an issue. This keeps reviews focused on implementation.