Are all the members of the literature committee fluent in the languages of all the works being evaluated? If not, how do they decide who gets to vote?
Short answer - no.
All 18 members of the Swedish Academy are allowed to vote, regardless of their proficiency in the language of a certain author. I’d be surprised if even one of them speaks Japanese, for instance, but that didn’t keep them from awarding the prize to a japanese guy, Kenzaburo Oe, some years ago.
Before the vote, however, all nominations are screened by a subset of the Academy known as the Nobel Committee, which narrows the number of nominees down to five. The committee are assisted by “specially appointed expert advisers” according to the official nobel site: