ADR-0034: Locale routing — /en/* for marketing pages only, not in-app routes

• Status: Accepted (2026-08-12)
• Prerequisites: ADR-0023 (default zh-CN + baseNavigator), ADR-0033 (bulk i18n conventions)
• Related: ADR-0025 (crawler UA split / OG reveal pages), ADR-0018 (CF Pages hosting), ADR-0003 (docs site already has /en/)

Context

www.erdonline.com is a pure CSR SPA; Chinese and English share the same URLs; language from umi_locale / browser language. For search engines one URL = one language version — English content is not indexable, hreflang has no URL, and English keyword organic traffic is blocked.

Full-site path localization would touch 60 routes, 76 history.push/replace, 236 E2E page.goto(), 16 backend URL configs, nginx bot rules, and immutable /s/:token short links. Login-required in-app pages have no SEO value; only /, /compare, /catalog matter (~21 internal marketing links).

Decision

Introduce /en path prefix for marketing pages only; in-app pages, /s/:token, /demo stay un-prefixed.

Item	Decision
Path scope	Slice 1: /en, /en/compare; slice 2: /en/catalog (list only; not /catalog/:id)
Implementation	Explicit English routes in config/routes.ts; LocaleRoute forces setLocale('en-US', false) on /en* and zh-CN on / — path overrides localStorage and browser language
In-app pages	No prefix; 76 history.push and 236 page.goto unchanged
First visit	English browser without explicit umi_locale and non-crawler UA → one-time history.replace('/en'); explicit switch writes umi_locale and stops auto redirect
Language switcher	Marketing: path jump (/compare ↔ /en/compare) + setLocale; in-app: existing setLocale
SEO	usePageSeo adds canonical, hreflang zh-CN/en/x-default, og:locale; frontend/public/sitemap.xml registers both languages
Prerender	Not now; 90-day Search Console gate before optional exportStatic for marketing routes only
nginx / backend	Zero change

Rejected: full-site /en/*; status quo; multilingual share/demo URLs; Accept-Language cloaking.

Relationship to bulk i18n

No blocking dependency; parallel. This ADR indexes marketing pages; ADR-0033 fixes in-app English retention. Order: slice 1 here → ADR-0033 extraction → slice 2 /en/catalog.

Consequences

• Positive: first independently indexable English URLs; small change surface.
• Cost: marketing vs in-app locale rules differ; sitemap maintenance.
• Risk: UA regex must stay synced with nginx.conf; 90-day CSR indexing gate may trigger SSG slice.
• Verification: Googlebot curl 200 + hreflang; E2E /en English + / Chinese; en browser first visit redirect once, explicit zh switch stops redirect.