Hmm.. That's odd, based on the manual that you can download on Doro PhoneEasy 506 page, it should be there. Can you confirm if the wrench icon on the menu is Settings?
Ahh.. The options are also in Dutch. Here's what I got from Google Translate.
Ok so, go to Settings > "algemeen" > "taal" or "spraak". Hope that helps.
Thank you, the option 'language' isn't there! My mum put the phone on charge, and when she removed it, the language has changed to Dutch, and the option to change language can't be found?