language error appointment confirmation

My website is multilingual (English/Dutch) and i'm trying to set up an appointment page using Appointment+. The Dutch appointment page works fine using the .mo/.po translation files.

The English page however not: after selecting an date and time, this page is showing the following things on the confirmation field in Dutch (instead of English):

- Name provider - ....
- Service - ......
- Date & time - ...........
- Duration - ......

The entry fields including name, phonenumber etc. are all shown correct in English.
I used the [app_confirmation] tag without any adjustments. When removing the .mo/.po files, this restores in English.

How can this be fixed?

[IMG]http://i57.tinypic.com/21ct3rq.jpg[/IMG]