The TeamCal Neo menu offers the option to change the display language for the current session. It will be reset to the default language the next time you log in.
If you want to use a different language than the default every time you log in, you can configure it in your profile settings.
Select Edit Profile from the user menu and select the Options tab. You can select your own default language there.
As an administrator you can select the default language in the Framework Configuration on the General tab.
TeamCal Neo comes with two languages, English and German. Creating a new language is fairly easy by translating the English language files into the language of your desire. Ask your administrator about it.