Problem

My browser setting:

Accept-Language: fr-FR,fr;q=0.9,en-GB;q=0.8,en;q=0.7,vi;q=0.6,ja;q=0.5

My MBS selected language:

Cookie: {…}; lang=en

Using any external release editor seeding*, release editor page is displayed in French instead of English.

* External release editor seeding

Here is the easiest way:

1. Go to MBwiki:Development/Release_Editor_Seeding and save seed-love-bug.html locally
2. edit action="/release/add" into action="https://musicbrainz.org/release/add"
3. Run it locally and press the seed button

Or it's also the case with Picard Add Cluster As Release plugin or Discogs Importer, the two things that I have spotted that made me try to fix this.