Something like this should get you where you need to be. The only other thing is to create a custom macro method that will look up with value in the other table, and return the name. The documentation walks you through creating your own macro method.
https://docs.kentico.com/display/K9/Registering+custom+macro+methods
{% y = PracticeArea; foreach (x in y){z += MyCustomLookupMacroMethod(x); } return z; |(identity)GlobalAdministrator%}