Hi Joost,
If you mean distinct testimonials for each language without translated versions, then you will need to create categories for each language and assign the testimonials to its category manually. Then create a separate view for each category.
The Multiple Forms add-on would allow you to create a separate form for each language and assign the testimonial to the corresponding category automatically.
https://strongplugins.com/plugins/strong-testimonials-multiple-forms/
Following up for those who may stumble upon this topic.
To have separate testimonials for multiple languages (only English, only Dutch, etc.) you need a category for each language and pair of views for each language. One view in form mode to assign testimonials to a category, and another view to display that category.
http://www.screencast.com/t/QFzF4XPa
The forms will share the same set of custom fields, which can be translated via WPML. The Multiple Forms add-on is only necessary if you need different custom fields per language.
