Wrong language on the OnBoard Computer?

First you have to unlock the OBC. To do that, press the '1000' and '10' button at the same time. This results in a 'Test' message on the OBC display. Now use the '10' and '1' buttons to select the test mode you need to unlock the computer, which is '19'. After that press the S/R button. Now you must enter the code that will unlock the OBC, which is the sum of the current day and month, so if today is the 10 day of the 11 month (10. November), the sum is 10+11=21, so you enter the number '21' using the '10' and '1' keys. Press S/R when done.
Enter test-mode again using '1000' and '10'. This time you want function 11 to select the Language mode, so you press '10' and '1' one time each and press S/R. The readout will be 'LA-' (meaning Language) and then the selected language code. Use the '1000' and '100' button to select the preferred language. Finish with the S/R button.
Switching between kilometers / miles - Celsius / Fahrenheit and so on is easy, just press the button to the left of the OBC display. Please note that you will have to do this for every mode like Watch, Distance, Temperature, Limit...