"Luke, tell your uncle if he gets a translator, make sure it speaks Bocce!" - Beru Lars to Luke Skywalker, in Star Wars Episode IV: A New Hope, Blue-ray edition.
Wookieepedia describes Bocce as such:
Bocce was an interplanetary trade language comprising parts of multiple languages. It was created by the Baobab Merchant Fleet to allow communication between starcraft pilots, crews, and support personnel of various species. Though not commonly used by most, any experienced pilots or spacers would know a few Bocce phrases in case they came across those that did not speak the pilot's native language.
But Larses were moisture farmers. They didn't seem to fly/trade off-planet, and clearly from the rest of the movie Bocce isn't necessary to communicate on Tatooine (even in Mos Eisley unless one talks to alien spacers, which a moisture farmer isn't likely to do - they'd probably sell the water to some merchant/water seller and not to individual pilots, if you think logically about basic economics).
Is there any plausible explanation in-universe as to why Larses wanted a specifically-Bocce-speaking translator droid? (any canon level).