Here are the two arguments I hear most often.
First, people say that bilingualism is not a skill and that we should, therefore, support judges who have the best knowledge of the law or who have a particular expertise, rather than judges who are bilingual.
To that I say that bilingualism is, in fact, a skill. Judges are asked to interpret bilingual pieces of legislation, so they must be able to understand the hearings held before them in one language or the other and to make their own analyses by reading their own documents.