The Fritz MT-F phones are shipped with German language as default, firmware version 1.02.27. It will come up with German message to register alternating with the English message:
If left for a few minutes it will show “not registered” in English and alternate to German
When the MT-F is registered to a fritzbox with internet access it will switch to English and update to the latest firmware. From then on it will be in English even if reset to factory defaults.