@UntrustableRus I think that Sanguine said that custom domains will be temporary unavaliabe during the upgrade. But they should work now, since they are upgraded and migrated. The message "we are looking into it" could mean that the system was noticied about the bug. I'm sure it will be resolved soon.
@RobTheDevRBLX yes, that happens to me too. I'm pretty sure that the installation went wrong, but this might be fixed fast too, aswell.
@Sanguine right now, I'm also making a Slovak language extension, and my question is if you can add it directly from the GitHub repo. I have never done any extension before, and a lot of have the "composer" thing, which I have not setup. I forked the English language (flarum/lang-english) and edited text strings there.