Handle invalid locale in the `Accept-Language` request header

[robotdan]

Description

If you send an invalid locale value such as en_AE instead of en-AE in the Accept-Language header, we should ensure we handle this correctly.

MDN suggests returning a 406, or to just ignore the value.

The server possibly can send back a 406 (Not Acceptable) error code when unable to serve content in a matching language. However, such a behavior is rarely implemented for a better user experience, and servers often ignore the Accept-Language header in such cases.

Related

• Sending an invalid locale in the Accept-Langauge header to /oauth2/token returns 500 fusionauth-issues#1958

Additional details

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language
• https://httpwg.org/specs/rfc9110.html#language.tags

[robotdan]

Fixed in 0.1.10.