hieroglyphics in menu instead of text

Hello everybody,

I have a fresh Ubuntu 16 installation with Libre 5.1.2.2.
Instead of having a menu text, I see hieroglyphics e.g. when opening the paragraph option.
The problem occurs in other positions of Libre as well.
Reinstalling didn’t helped so far. Does anybody know about this problem?

Thank you very much for the help.
(So far I do not have enough reputation to upload a screenshot, sorry)