It's established that C-3PO can speak the Huttese language, as he does at the gate to Jabba's palace, but when he is performing his interpreting duties for Jabba (for example, when Jabba is negotiating with Leia, disguised as Boushh the bounty hunter), he translates whatever language is being spoken into Basic (shown to us as English).
Why?
Jabba can obviously understand Basic when it's spoken to him, but it's clearly not his native language. Doesn't this seem inefficient, and potentially rude? I can understand the filmmakers wanting to minimize the portion of the movie that requires subtitles, but there's enough Huttese dialog already that it seems like this would be fairly marginal.
Thoughts?