Client Locale and MPQ Files

I'm working with World of Warcraft Emulators for about 4 years. Mostly I write scripts and new core features.
Now I want to start with client modifications in general.

The first thing I did were simple DBC changes e.g. adding new titles, spells or currencies.
I'm currently using an enGB client. All changes had worked without any problems.
Now I gave the MPQ file to a friend who is using the deDE client. He was able to launch the client without any problems but e.g. the added titles were show as questionmark.

I know that the DBC files have different locales but why got my friend the questionmark title instead the english version "Test Title %s"?

It is possible to write a MPQ which supports different locales?

Thanks in advance!