It may happen that after a factory reset, your handset turns on in German. Follow this procedure to change the language of your handset:
Navigate to " Menu -> Setup / Einstellung -> Phone Settings / Geräteeinstellungen -> Language / Sprache -> Handset language / Anzeige-Sprache and choose the language you wish to use.
Here are the available languages:
Deutsch
English
Francais
Italiano
Nederlands
Русский
Magyar
Español
Polski