I have to make up a topic for my master´s thesis

related with comparative linguistics (Polish and Spanish) or with comparative analisis of Polish translations of Spanish books or Spanish translations of the Polish ones.

I do not know what may be both different from Polish and interesting in writing about in Spanish language.
My language has less tenses but two versions of verbs for perfective and imperfective aspect, no articles, prefixes which modify the meaning of verbs, gramatical cases etc. - But if I choose something related with that I would have to limit my thesis to something smaller and I have no idea to what.

Other topics could be on fraseology, colloquialisms, neologism, arcaisms, etc - but I do not know where I could find Spanish books including many examples of these.

Any idea?