How can I detect the default locale based on the URL when using localePrefix = 'as-needed'

[staffanmowitz]

I am working on a project that involves two languages: Swedish and English. I am using prefix-based routing with localePrefix set to as-needed, where Swedish is the default language. When manually switching the language to English and accessing a Swedish URL, /test, it redirects to /en/test.

As per the documentation, the locale detection process works like this:

1. A locale prefix is present in the pathname (e.g. /en/about)
2. A cookie is present that contains a previously detected locale
3. A locale can be matched based on the accept-language header
4. As a last resort, the defaultLocale is used

Since my setup lacks a locale prefix in the URL pathname due to localePrefix being set to as-needed, next-intl will move on to the next step and detect the locale from the cookie.

Is there a way to make next-intl recognize URLs without a locale prefix as Swedish and change the locale accordingly?

[amannn]

Sure: localeDetection: false

[staffanmowitz]

Thanks for the quick reply!

I still want to keep the ability to detect the locale from headers and cookies.

I'm basically looking for a way to detect that the locale is Swedish when there is no locale prefix in the URL.

Is this possible?

[amannn]

Hmm, I'm unsure I can follow how the locale negotiation should work in this case. Can you provide some examples of what you expect to happen for requests for a few pathnames, potentially with a cookie from a previous visit and considering locale prefixes? Do you want to turn off redirects that consider a previous locale for all pathnames but the root of the app (/)?

But to answer the question, you can compose the middleware and read a potential locale prefix from the pathname, similar to how it's shown in the additional rewrites example. Based on that, you modify the request (e.g. remove/set a cookie) or use that information to configure the next-intl middleware on a case-by-case base.

Does that help?

[staffanmowitz]

The problem occurs when a user who has previously visited the site, and has the cookie set to en, tries to visit a page with Swedish locale, i.e. a URL that has no locale prefix in it.

For example, I have a Swedish news article with the URL example.com/nyheter/nyhetsartikel. If the user visits this URL but has the cookie set to en, they will end up on the URL example.com/en/news/nyhetsartikel, which does not exist. If the user does not have the cookie set to en it works as expected.

I have read the documentation on how to configure the middleware matcher to detect pathnames without locale prefixes and applied the suggested matcher pattern, but I still can't make it work.