"He will have created a center."
Translation:Hij zal een centrum gecreëerd hebben.
No, not all separately. The trema means that this particular e is pronounced separately from the whole word. So actually it says gecre-eerd, but this looks ever weirder ;) It is the same for all letters with tremas I think, for example ideeën (ideas), you pronounce the e with trema like it is separated from the word idee, so you pronounce idee-en.