@Albus
That's it - yes. But as Marco already pointed out, creating/altering tables can (and should be) handeled with product install/uninstall codes.
Also there is a function to create custom phrasetypes: add_phrase_type() in adminfunctions_language.php
Just the GUI is missing

I pointed this out @ .com, but the Devs don't seem to see a need for it.
For my needs, I ported
this Hack - makes it easy to handle Phrasegroups

I've contacted the author if he plans to release it, but did not get a reply so far.