There is the following problem/symptom, which may be also an idea for future development:

--> the invitation email for new users is in english only.

There seems to be no possibility to adapt this text.

Such text adaption is possible for other group-texts like group entry confirmation, 

group email denial. The text adaption are found in the group email-options.

The consequence of the english invitation email is, that new group users, expecially from outside the organization,

consider the group inviation mail as SPAM.

My idea would be to give the possibility to personalize the group invitation email.

Thanks for your thoughts!

Christoph.