What year is your vehicle? I believe on my 98 E320 I can change the language from the buttons on the instrument cluster. The procedure is in the owners manual. However, if your manual is in Japanese, following them might be difficult. If you have newer model with COMMAND with buttons on steering wheel procedure would be different anyway. Look for a link in the DIY section of www.benzworld.org for downloadable manuals in english for your MY. Your problem may also be regional and some languages may not be supported. Good luck

UPDATE:
If you have the function buttons on the edges of the instrument cluster at 9 o'clock and 3 o'clock
you can change the language as follows:

0 - Turn the key to the position '2' (last indent before starting)

1 - Simultaneously press the 'O' and 'R' buttons until the current language selection appears.

2 - Press the 'O' button until the desired language appears.

3 - Turn the key to off

As I mentioned language choices may be regional. In my US car I have English, French, German, Italian and Spanish. A car exported to the Far East may not have English as a choice.