What is the best way to approach a problem in which we want to, for a given locale, modify the address of the api we are hitting?

I would like to extend such a project with something like this
https://github.com/vercel/commerce

Currently it is simply env while on the basis of locale I would like e.g. this string of api address to modify somehow. The question is where?

https://erichowey.dev/writing/advanced-internationalization-with-nextjs-and-middleware/
I found such an article, in which the api address is edited in the middleware, and that's all right, but what about the requests that do not go this way such as POST and are sending it directly from the client