Sorry, I don't know what an umlaut is, but I did a quick google search on it, and I assume it's some sort of sign under or above a letter?
If so, can you use it in the normal contacts application?
Can you post a picture of?
If it's part of unicode, it should just appear, as I have removed all filtering.

Edit: I found some more info about it, i still need to know whats the status now, do you have contacts with umlaut? are they displayed in horizontal-call?
You can take a screenshot and upload it. Don't forget to blur any unwanted info.