Those two words were untranslated because their meaning in original was unclear - is it name of city/locality/region or something other. Assuming that “centre” is meaning “central point, main node of something” translation “центр” is correct. Also if Midwest - name of USA region, then translation “Средний Запад” is correct.
Ok, I checked Wikipedia, Centre should be “Центр” as it region name.
How can I test localisation in Navit? I have Android phone and PC, which one has most recent updates? Android version (installed yesterday) has old translation (and buggy as hell).
For testing langs, you need the recent SVN builds that already include the updated lang packages. Currently it’s done irregular http://sourceforge.net/p/navit/code/commit_browser but I will ask the Launchpad maintainer to do it this days.
Depending on your OS, it should be easier to update the PC instead of smartphone.