I think this depends on your goal with the projekt.
If your goal is to write a GUI in scala, then its no point in having a twitterAPI in scala.
if your goal is to write a full program in scala, then you should keep the api.
in the end it boils down to what you enjoy most, since its just to face the fact, your the one doind most of the coding. And since you ask the question, that shows abit that you prefer the gui part over the api part :-)
Yes there are some pretty nice twitterAPI's in java, havent tried them myself but i have heard good things.
I think the API is the most fun part. GUI's are best made with a gui-builder that scala lacks. but thats me and I have way to little time to do anything i want nowdays :-(
/Micke