for inlets/outlets I think we can use german words, but also mention the english terms, so that people are not totally helpless when they read english documentation.
in germany among germans I always heard Eingang/Ausgang, as well as
Nachricht.
I used "befehl" and "nachricht" for message. bibliothek for library sounds good to me, although I do not really use it. There are also some other terms that need to be translated, like box = ?
kÀstchen?
abstraction = ?
http://de.wikipedia.org/wiki/Objektorientierte_Programmierung has
Abstraktion
canvas = arbeitsbereich patch = ?