Add an extractor for the user language

[frenetisch-applaudierend]

• I have looked for existing issues (including closed) about this

Feature Request

Add an extractor for the preferred language for a user

Motivation

It is not uncommon to want to return a response in the users language, especially when building user interfaces. While it is not hard to implement this on your own, it is nevertheless some boilerplate code that could be avoided.

Additionally, having a canonical way to get the request language would allow other extractors and middleware to rely on that extractor to get the user language, e.g. to return localized error responses.

Proposal

Add a UserLanguage extractor that reads from the request a list of preferred user languages and makes them available for the user. Standard sources of languages could include the Accept-Language header, a :lang path segment and a lang query parameter.

It may make sense to make the language sources configurable as well as allowing to add custom sources, such as reading the language from a cookie.

Alternatives

This could also be implemented in a crate outside of axum. The advantage being less maintenance overhead for axum and allow for more diversity in implementations. The main drawback would be that there is no canonical way for library crates to read the preferred user language. Relying on a specific third party crate may not be desirable in such cases.

Implementation

If this feature is something that would fit into the scope of axum, I would like to contribute this in a pull request.

[davidpdrsn]

Sounds like a good fit for axum-extra. Then we can move it to axum when it’s matured.

[frenetisch-applaudierend]

Great, I'll take a stab at it then! Thanks!