After you have installed the application and before you start using it, check your settings. Go to the Settings application, then General, International. You will see something like this (without highlights of course):
Part 1: Settings
The language you see here, if it is English or Deutsch, is the language the application will use. Otherwise it will use English. If you like to support me in translating it to other languages, let me know.
Regional format affects whether metric or standard system is used (i.e. meters or feets).
Then return to the top level of the Settings application and find OSMTrack:
Select it and enter user name and password you use for the OpenStreetMap (theese are used to upload GPX traces):
You are done with the settings and can start using the app!