It seems to me that not being able to speak other languages tells you something about the level of education and breadth of knowledge of a person or at least about their open mindedness or lack of thereof.
Indeed. but like I said this is related to open mindeness, even if you don't know the other specific culture you at least have some sense of what things that your culture hold as unquestionable truths turn out not to be for "outsiders". making extrapolations with at least a good idea of another culture you are not part of is going to give you a way more reasonable explanation than estimating another culture with 1 datapoint.
I'm sure more than one of those people have issues with languages that some of the others are well versed in, and interpreters have been part of international diplomacy as long as there has been diplomacy.
The context is multicultural international relations. While it’s not impossible to have a good understanding of other cultures without learning their languages and reading relevant literature in the original language rather than a translation it’s highly unlikely.