Most of my Portuguese SF friends (the Tribe) only read SF in English. I’m one of those cases. But I also read Portuguese SF written in Portuguese. What I don’t do is read Anglo-Saxon SF translated into Portuguese. With a only a few exceptions, most of the guys translating SF into Portuguese are not conversant with the genre conventions. Forget it! The question of the prevalence of English-speaking authors in Portugal is thus unavoidable (because we don’t read SF in translation). In my view (and I presume, in the case of those with good judgment and enough SF reading in the bag), the notoriety of many authors who write in English is mainly due to the fact that this is the language that dominates the literary market around the world. I believe that if many of these Anglo-Saxon SF authors were Portuguese, born in Portugal and writing in Portuguese, hardly anyone would hear of them because they wouldn’t stand a chance in hell of being published.
If you're into SF and SF conventions in particular, read on.