I never worked with a ZMMH1 structure, but the standard structure BMMH1 has as well the description field and does not have a language field.
It is just so that BMMH5 must only have entries for other languages than your logon language.
So just exchange E to D and EN to DE in BMMH5 and try again.
I expect that you then get your material with English and German language. If that is the case, then you know that you can skip BMMH5 if you only need one language in your material master