"The language you specified is not valid." when editing preferences

[redsquirrel]

I have an issue with user control panel when editing preferences, it says the language specified is not valid, but there is also not an option for language. This may possibly be something I did wrong somewhere down the line in dev but wondering if anyone has an idea of what I can check to see what would be causing this. I only have British English as a language pack so that should just be the default. I don't care so much about that part but this error makes it so people can't change their time zone setting.

[rxu]

This may happen when the lang iso entry selected in UCP doesn't exist in phpbb_lang table for some reason.

[redsquirrel]

Thanks turns out it was exactly that! They were all blank. When I imported the users I never even thought of that field. I set all users to 'en' in dev and it fixed the issue so will do it in prod once I check things further.