Innostream

I bought the exellent INNO 55 in Thailand.
After i come back in Germany i use my German SIM card.
After lock in, the language changes automaticly to Thai Language and i cannot change the language.
When i am using a Thai Sim card i can change the language to english again.
Strange thing is with the German Sim card i can make phone calls and use every feature of the phone. Only the language changes to Thai.
Have anybody a idea what i can do?
I am afraid that the Phone is somehow "locked" for foreign sim card.
Thanks in advance
Thorsten