Ignoring accept_language in localization middleware based on prefixed URL patterns

[Janez Kranjc]

Hi guys! I’m Janez Kranjc, I’ve been using Django for a bit now - since 1.3 and I’ve recently come across and issue that’s been bothering me in multiple projects that I’m working on.

Localization middleware ignores the accept language header if ANY url pattern exists that is i18n prefixed regardless of the current URL of the request.

So the problem is the following: I have some URLs that are prefixed, and a lot that are not (such as all of the API endpoints). I sometimes need to return some translated strings in the API as well and for that I rely on the accept-language header. However in the middleware it is ignored because an unrelated part of the project has an i18n prefixed url pattern.

Another way to look at the problem is this:

Let’s say I have a SPA that uses i18n on its API endpoints and you rely on accept-language to serve the responses in the correct locale. I then decide to add a new app to your django project - a sales page. Instead of relying on accept-language I wish to have i18n prefixed URLs (maybe for SEO reasons or whatever). Suddenly the behaviour of the API changes even though I’ve made changes to an entirely different part of the project.

Would it not make more sense for the middleware to check if the current URL pattern (the one that the request URL resolves to) is prefixed or not.

The way I see it, this should be changed:

i18n_patterns_used, prefixed_default_language = is_language_prefix_patterns_used(urlconf)

Instead of checking the entire urlconf it should only check the current request URL and see if it resolves to a pattern that is i18n prefixed.

To get around this I need to use a custom localization firmware in a lot of my projects. I would like to hear the devs’ opinion regarding this.

[Aymeric Augustin]

Hello,

Yes, I think this change makes sense, assuming no unexpected difficulties arise in the implementation.

Best regards,

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Aymeric.

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[Aldian Fazrihady]

What prevents the change to the API endpoints so it will have language prefix as well?

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Regards,

Aldian Fazrihady
http://aldianfazrihady.com

[Janez Kranjc]

Nothing prevents the change to the API endpoint except the fact that users are actively using the API already and (it is my opinion) that a change in another part of the application - like a sales page - shouldn't affect the working of an unrelated part of the project. Also that would mean refactoring the front-end code which uses API endpoint to use different URLs instead of just adding a header.

Imagine that I have a third party app and I include its URLs and they have prefixed URLs (unlikely but could happen) - this would force me to change the way my URLs work in order to have a multilingual API.

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[Janez Kranjc]

Another problem that is specific to APIs (which are not really the point here, just an example) is that using prefixed URLs that has the default language also prefixed - prefixing API urls during the lifetime of the application would break the API for specific users because the previous URLs would 302 to new URLs and all POST requests would break. But like I said - an API is just an example I'm using to illustrate my problem. Could be any part of an application.

[Janez Kranjc]

So regarding the implementation my proposal is this:

instead of checking if a prefixed url pattern exists, resolve the current request path to a pattern and check if it is i18n prefixed

any idea how much of a performance hit that would be? Because right now we're accessing a cached variable, which is super fast. With this implementation there's a bit more work that the server needs to do in the middleware. The problem is that URL resolving takes place after the middleware so even resolver_match is not yet available when we need it. Any suggestions?