Outside of the Teimanim I am not aware of any other segments of Judaism that still employ a meturgamen (translator) during kriat ha'torah. Why has this practice fallen into disuse?
The Shulchan Aruch OC 145:3 says that:
Additionally, the Tur there quotes a Yerushalmi that says that the meturgeman is not me'ackeiv (prevents the fulfillment of the mitzva of reading the Torah).
Also, Tosfot (Megillah 23b sv Lo) learns from the gemara there that even at the times of the gemara, only some places had meturgemanin and some did not, implying that it was only a custom, not an obligation. This helps explain why we can just drop it when it doesn't serve it's intended purpose.
I'm told there are Sephardic communities in which an Arabic translation was read until not long ago.
I've heard that Rabbi Joseph Dov Soloveichik proposed the following reason for the cessation of translation in Ashkenazic communities: in many towns in Medieval France & Germany, there weren't that many knowledgeable people around, so the translator himself would have had to rely on a printed translation into Old French or the like. The only (prevalent?) such translations were Christian ones which may have pushed a very Christian understanding. Hence the practice of translation was discontinued.