docs: publish translated docs in twelve languages and the tool that maintains them

.github/workflows/deploy-docs.yml

@@ -12,6 +12,8 @@ on:
       # docs pages include their code blocks from these files via `--8<--`, so a
       # change here changes the rendered site even when no .md file moves.
       - docs_src/**
+      # translated pages and the language registry feed the site/<code>/ sites
+      - i18n/**
       - mkdocs.yml
       - src/mcp/**
       - src/mcp-types/**

.github/workflows/docs-preview.yml

@@ -21,6 +21,7 @@ on:
     paths:
       - docs/**
       - docs_src/**
+      - i18n/**
       - mkdocs.yml
       - scripts/docs/**
       - pyproject.toml

.gitignore

@@ -144,10 +144,13 @@ venv.bak/
 # documentation
 /site
 /.worktrees/
-# Generated at build time by scripts/docs/ (the API reference tree and the
-# concrete Zensical config spliced from mkdocs.yml).
+# Generated at build time by scripts/docs/ (the API reference tree, the
+# concrete Zensical configs spliced from mkdocs.yml, and the staged docs tree
+# of each translated site).
 /docs/api/
 /mkdocs.gen.yml
+/mkdocs.*.gen.yml
+/.build/
 
 # mypy
 .mypy_cache/

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 --pages` 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.

docs/js/language-switch.js

@@ -0,0 +1,31 @@
+// The theme links each language-switcher entry to that language's home page.
+// Point the entries at the current page on each language's site instead: every
+// prose page exists at the same path on all of them. The API reference is
+// English-only, so from there the entries keep pointing at the site roots.
+// Instant navigation swaps the page but keeps the header, so re-run on every
+// page the theme loads (`document$`) rather than once.
+const base = JSON.parse(document.getElementById("__config").textContent).base;
+// The site root as a directory path; `base` lacks the trailing slash on 404 pages.
+const site = new URL(base.replace(/\/?$/, "/"), location).pathname;
+const entries = ".md-select__link[hreflang]";
+
+function samePage(entry) {
+  const page = location.pathname.slice(site.length);
+  return entry.dataset.site + (page.startsWith("api/") ? "" : page);
+}
+
+document$.subscribe(() => {
+  for (const entry of document.querySelectorAll(entries)) {
+    entry.dataset.site ??= entry.getAttribute("href"); // the language root the theme rendered
+    entry.href = samePage(entry);
+  }
+});
+
+// Headings carry the same ids on every site, so the reader's place carries over
+// too: query and fragment as they are when the switch happens, not at page load.
+function aim(event) {
+  const entry = event.target instanceof Element ? event.target.closest(entries) : null;
+  if (entry?.dataset.site && (event.type !== "keydown" || event.key === "Enter"))
+    entry.href = samePage(entry) + location.search + location.hash;
+}
+for (const type of ["click", "auxclick", "keydown"]) document.addEventListener(type, aim, true);

docs/translations.md

@@ -0,0 +1,25 @@
+# Translations
+
+This documentation is written in English. To make it useful to more people, we also publish machine-translated editions of it, and this page explains what that means for you and how to help improve them.
+
+## What's available
+
+Translated documentation is currently a **preview** in twelve languages: Deutsch, español, français, हिन्दी, 日本語, 한국어, português (Brasil), русский язык, Türkçe, українська мова, 简体中文 and 繁體中文. Pick one from the language switcher at the top of any page. More languages may follow once these have proved themselves.
+
+The API reference is not translated: the translated site links to the single English one.
+
+## English is the source of truth
+
+If a translated page and its English original disagree, the English page is correct. Every page of a translated site opens with one of three notes saying where it stands:
+
+- **Machine translation** — the page was translated automatically and links to its English original.
+- **Translation behind the English page** — the English original changed after the page was translated, so parts of it may be out of date until the translation catches up.
+- **Shown in English** — there is no current translation of the page, so you are reading the English text.
+
+## How the translations are made
+
+Translated pages are machine-generated by a tool in this repository from the English pages under `docs/`, guided by two human-written inputs per language: a style guide (register, tone, typography, how to handle jokes and idioms) and a glossary (which terms stay in English, and the required and forbidden renderings for the rest). The generated text is never edited by hand. Every improvement goes into those inputs instead, so it survives the next time the pages are regenerated.
+
+## Reporting a translation problem
+
+Found a wrong term, an awkward sentence, or a translation that says something the English doesn't? [Open an issue](https://github.com/modelcontextprotocol/python-sdk/issues) with the language, the page and the passage; reports from native speakers are especially valuable. If you know the fix, propose it directly as a pull request against that language's style guide (`instructions.md`) or glossary (`glossary.json`) under [`i18n/`](https://github.com/modelcontextprotocol/python-sdk/tree/main/i18n) — the correction then reaches every affected page the next time the translations are regenerated. Problems with the English text itself are fixed in the pages under `docs/`, like any other documentation change.

i18n/README.md

@@ -0,0 +1,20 @@
+# Documentation translations
+
+The English pages under `docs/` are the source. This directory holds what steers their machine translation and the generated result; [`docs/translations.md`](../docs/translations.md) is the reader-facing explanation.
+
+- `languages.yml` — the registry: one entry per translated site (served at `/<code>/`), the model id, and the nav pages that stay in English.
+- `general-prompt.md` — translation rules shared by every language. `notices.md` — English source of the three notes staged onto the pages of a translated site.
+- `<code>/instructions.md` (register, voice, typography, terminology) and `<code>/glossary.json` (`keep`: terms that stay in English; `terms`: required renderings, each with an optional `note` and banned `avoid` renderings, which are checked) — human-authored, sent with every request.
+- `<code>/pages/**` and `<code>/notices.md` — **generated**, never edited by hand: a correction goes into that language's `instructions.md` or `glossary.json` (or the English page), and the affected pages are re-run.
+
+## The tool
+
+```text
+uv run --frozen python scripts/docs/translations.py status [--lang CODE]
+uv run --frozen --group translate python scripts/docs/translations.py translate --lang CODE [--pages PATH ...]
+uv run --frozen python scripts/docs/translations.py stage [--lang CODE]
+```
+
+`status` is offline: per language it lists missing, outdated (with the sections that changed), current and removable pages (translations whose English page is gone — `git rm` them). `translate` calls the Claude API (`ANTHROPIC_API_KEY` in the environment; the registry's model, or `DOCS_TRANSLATE_MODEL` to trial another) for the missing and outdated pages, retranslating only the English sections that changed and keeping the rest byte for byte; `--pages` instead re-translates exactly the named pages from scratch, which is also how a glossary or instructions change reaches existing pages (each generated page records the English section hashes it reflects, so editing those inputs invalidates nothing). `stage` assembles the tree each language site is built from (every language's, or one with `--lang`); `scripts/docs/build.sh` runs it before building them. Commit the generated pages in an ordinary pull request.
+
+To add a language, add an entry to `languages.yml`, write `<code>/instructions.md` (the sections the `pt` file has) and `<code>/glossary.json`, then run `translate --lang <code>`.