I think that many of the posters have no clue what it meant to travel in those days and the difficulties it entailed. Allow me first to correct some factual mistakes.
yichusdik: Rashi did NOT live in the places that you mention. He lived most of his life in Troyes-which is in the middle of France. He learned in the area you are quoting (worms, actually) so, at best, he knew some german and, of course, Old French.
Also, the Plantagenets did NOT rule that part of france- as a matter of fact, Rashi died in 1105 ,when the Plantagent dynasty had not started yet.
Arabic was unknown to Rashi- he never traveled to Spain and, probably, castilian Spanish was also unknown to him.
To WIY- again, you elevate Rashi to be a Novih. Rashi was the greatest “meforosh”on shas- and one of the greatest Jews that lived but this doesn’t make him infallible nor does it make his words always correct (there are plenty of “kashas” from his own grandchildren, the baalei tosefos).
In any case, this is not even an opinion by Rashi ,it is just a description of an item and it is ludicrous to say that Rashi did not make a mistake in namimg the wrong item.