Because the URL to the filter form is hardcoded in javascript path prefixes aren't added, breaking language negotiation. This will always show the form in the default language (depending on your fallback).

How to reproduce (and get the best effect):
- Configure your language negotiation to only use path prefixes
- Set your default language to something other than English (in my site it's Japanese)
- Configure path prefixes for all languages except the default language
- Browse the admin in a non default language
- Open the filter form and you'll see it's shown in the default language (Japanese in my case)

Attached is a patch that adds the url as a javascript setting.

CommentFileSizeAuthor
filter-url.patch3.71 KBstijndm
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