jacko Yes, I get the feeling that could be the cause of the problem.
In fact, it would be best if Flarum didn't allow you to disable a language pack that's being used as the default language for the forum. But I don't think Beta 2 bothered to check for that.
Is this line of thinking making any sense @Toby ?
EDIT: I've gone ahead and revised the upgrade instructions in any event, since it's probably a bad idea to have the forum's default language set to a language pack that's disabled:
- Disable all extensions. (If you've set a language other than English as the default language for your forum, be sure to set the default language back to English before disabling the language pack!)