Greetings .)
We've tried to add some cyrillic symbols on "Customise the "Powered By" header sent by NodeBB" field in Avanced settings. After saving - it dropped the entire forum with admin panel itself.
Got error:
[ [global:500.title]]
[ [global:500.message]]
The header content contains invalid characters.
Solved only via manual removal of this field in redis base.
Is it a bug or...? 
Sounds like a bug, please post the content you used for the header.
МойОфис
I want to note that cyrillic symbols in Title field works properly.
Seems to work fine
Is that the entire content you put in that field? Do you get any errors in your nodebb logs.
Same entry in logs. The header content contains invalid characters. We've tried to add МойОфис both manually and via copy/paste so there's no possibility of adding some special symbols exept cyrillic.
