Q: How can I set my language to dutch instead of french in Belgium?

Sorry, but you can't. The language of the movies is that provided by the movie studios and unless they provide different versions cannot be changed. If you wish subtitiled original versions of the movies, contact the movie distributors in Belgium and urge them to make them available in the iTunes Store.

Regards.

You can't. The Belgium iTunes Store is available only in British English or in French. But that shouldn't prevent you from purchasing a movie in the original version with subtitles if it's available in the Belgium iTunes Store. Are you sure another version is available in the Belgium iTunes Store, or are you referring to the version being available elsewhere?

If you want the iTunes Store in English, see:

http://support.apple.com/kb/HT2242

To comment to Apple on the lack of a Dutch option, you can use the Feedback page:

http://www.apple.com/feedback/itunesapp.html

As to the movie content, though, again that's the choice of the movie studios. Apparantly they also think Belgium is exclusively French.

Regards.