The Problem was that the user had a script blocker activated. Is that something that must be supported nonetheless?

I don't know what ajax-y Phabricator actions are. The guy can comment commits and audits and everything just fine, though. Will check the other things you mentioned tomorrow

That would be exactly what I need here.

Commenting on the initial discussion: "You need to know English to write almost any code anyway."
I think that although one must be fluent enough in english to write code, the other features do not necessarily have that 'restriction'. At our place we could use Maniphest and its Board features for organizing non-coding work. However, some of the people which are involved would have a very hard time understanding the english interface