Well, one the most common -ling word is "Earthling", which in Portuguese is "terráqueo".
Otherwise "-ling" refers to either a diminutive (princeling, duckling), and thus being tanslated as "-inho", or to someone to whom something concerns (hireling, underling, which are traslated as "contratado" and "subordinado").
The tief- prefix is made up, even if it is inspired by Teufeul. If it were Teufeling, the translation would be "diabinho/capetinha" or "endiabrado/encapetado", neither of which is very interesting. Also, note that "tief" in German means "the deep", so a "tiefling" would be "from the deep" (meaning, from the Pit).
If you go by this definition, it opens words like "abissal", "abismal", "aprofundado", which sound a bit better (you could reserve "abismal" for things from the Abyss and have "abissal" for tieflings).
Another great words for things from the depths of the Earth, specifically gods from the deep, is "ctoniano" or "ctônico". Echoes of Cthulhu abound!
BTW, I was thinking about the warpriest, and you could use the word "eclesiástico" for the class. This way the PHB cleric (templar) would be a "clérigo templário" and the Essentials cleric (warpriest) would be a "clérigo eclesiástico". Makes sense if you think that the warpriest is devoted to a divine domain, and has only Wisdom attacks, while the templar is devoted to a god and has Wisdom AND Strength based attacks.