Assign the preferred localized URL key to each CMS page, e.g.:
EN: about-us to cms/page/view/page_id/1 titled About us
NL: over-ons to cms/page/view/page_id/2 titled Over ons
DE: ueber-uns to cms/page/view/page_id/3 titled Über uns
Create custom permanent redirects (Marketing -> URL Rewrites) for the keys foreign to the Store View:
EN: over-ons to ...