HTTP headers
Accept-Language HTTP Header Meaning
Accept-Language tells the server which languages the client prefers.
Meaning
The client is sending a prioritized language list for content negotiation.
Where it appears
Browsers send it when sites may choose localized content automatically.
What to check
Check whether the response language is chosen intentionally and whether Vary includes Accept-Language.
Example
Accept-Language: en-US,en;q=0.9