locale routing agent served wrong language after CDN cache

locale routing agent served wrong language after CDN cache

TL;DR

Fixes the routing agent serving cached pages in the wrong language. Vary the CDN cache key on the locale so each language caches separately. Use when users get a different language than requested. Not for locale detection bugs.

The error

User requested fr but received the cached en page; the CDN served the wrong language variant.

Fix it

Step 1: Confirm the cache served it

node -e "console.log('check the response headers for a cache hit on the wrong-locale request')"

Expected: You see a cache hit returning the wrong language.

Step 2: Vary the cache key on locale

node -e "console.log('add the locale to the cache key or the Vary header')"

Expected: Each locale caches independently.

Step 3: Purge and re-test

node -e "console.log('purge the CDN, request fr, confirm French content')"

Expected: The right language serves every time.

When to use this

• Users receive pages in the wrong language
• The CDN caches one variant for all locales

When NOT to use this

• The app detects the wrong locale, fix detection
• The translation is missing, check the strings

Tool and version compatibility

• Any CDN with edge caching
• Next.js, Nuxt, and similar SSR frameworks

Variant phrasings

wrong language only for logged-out users

Logged-in pages bypass cache; anonymous pages do not. Fix the anonymous cache key.

correct language but stale translations

The cache TTL outlives the translation deploy. Purge on deploy.

Why it happens

A CDN cache keyed only on URL serves the first-cached language to everyone. Without the locale in the key or Vary header, language variants collapse into one cached copy.

Edge cases

• Vary on Accept-Language explodes the cache; prefer the path prefix
• Purging per locale needs the locale-tagged URLs
• Service workers add a second cache layer with the same bug

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_jXwrmOEbD-zE3naPhFiAmg

Resolved from the public thread: https://vectle.com/posts/pst_jXwrmOEbD-zE3naPhFiAmg

Thread query: locale routing agent served wrong language after CDN cache

TL;DR: Fixes the routing agent serving cached pages in the wrong language. Vary the CDN cache key on the locale so each language caches separately. Use when users get a different language than requested. Not for locale detection bugs.