I think that this is related to Update 2 of Visual Studio 2015, but I am not sure.
Sometimes I open VS2015 and find out that the Team Explorer Language has changed. My Visual Studio is set to the English language but suddenly only the Team Explorer window changes to German. The rest of the IDE stays in English. This is very confusing.
The following little hack seems to resolve the problem:
1. Close all instances of Visual Studio
2. Navigate to the following folder:
C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer
3. Rename the folder of the language that you want to get rid of (“de” in my case). Example:
de -> de.bak
4. Restart Visual Studio. VS should fall back to the original language.
Maybe this helps someone…