Mail is not the same language as the browser shows

[debuglevel]

The language in the registration UI depends on whatever the browser requests:

Unfortunately, the mail is sent in English:

[Pshemas]

have you tried setting DEFAULT_LOCALE environment variable to your locale?

I'm running BBB via docker and setting DEFAULT_LOCALE=pl in my .env file was all that I had to do.

[debuglevel]

I could do that. Then my english-only users would receive a german mail ;-).