There aren't a lot of great options when you hit a brick wall. Few professional genealogists have any experience in the field (my inability to read German causes me problems...). You really have to piece together information from a lot of sources. However, I do have some places to start.
1. Translation: The APG Directory allows you to search for translators. Have some patience... There's currently no option to search for a specific language.
2. An American brick wall: Consider contacting the local historical society or town/village historian. You'd be surprised how well they know the local families.
3. A Luxembourg brick wall: Yes, there are professional historians in Luxembourg. A Google Search will turn up a few names. Disclaimer - I haven't hired anyone.
And you can always ask a question. I'll do the best I can!