Symptoms
The title of the main window in Microsoft Skype for Business 2016 should always display "Skype for Business" in the language that you selected during Microsoft Office setup. With that in mind, assume that you set the default language to German for Skype for Business 2016. However, when you start the client, the title bar displays "Skype for Business" in Russian instead of German.
Resolution
To fix this issue, install the March 8, 2016 update (KB3114846) for Skype for Business 2016.