docs: send readers to their language and list translated sitemaps

[devGregA]

What

Language redirect. A reader who arrives on an English docs page from outside the site now lands on the same page in their language, if that page has a translation. The language comes from:

1. The language they last picked in the header language menu (saved in localStorage).
2. Otherwise, the first of their browser's preferred languages that we translate. If English comes first in that list, they stay on English.

It never redirects:

• clicks within the docs, so a reader can pick English from a translated page and stay there, and the untranslated sections that translated pages link to (releases, supported_tools) don't bounce back
• crawlers
• pages without a translation

Traditional Chinese browsers stay on English rather than going to Simplified. All Portuguese variants go to pt-br. The redirect uses location.replace and keeps the query string and anchor, so the back button never loops.

Sitemaps. The root /sitemap.xml only lists English pages. Each language has its own /<lang>/sitemap.xml, but nothing pointed to them. robots.txt now lists all eight.

Why

Two weeks of site analytics show that few readers find the translations. For example, 93 docs visitors had German browsers but only 8 opened a German page. Each page already has correct hreflang tags. The gaps were search engines never being shown the translated sitemaps and readers never being sent to their language.

Testing

• Production build (hugo --minify --config config/production/hugo.toml) is clean.
• The script appears only on English pages that have translations (checked the home page and a guide page). It is absent from translated pages and from untranslated sections.
• Ran the built, minified script against 18 cases using mocked browser objects. Results: de-DE, fr-CA, pt-PT, pt-BR, zh-CN and bare zh redirect to the right language. en-before-de, zh-TW, zh-Hant-TW and ko-only stay on English. A browser listing ru then de goes to de. A saved en beats a German browser, and a saved es beats a German browser. An internal referrer doesn't redirect, while an external referrer from Google does. Googlebot doesn't redirect, and query plus hash are kept.
• Clicking a language in the header menu saves it, and clicking other links doesn't change it.

🤖 Generated with Claude Code