Rashi was actually quite an accomplished linguist. He lived in a border area often in dispute between Champagne, Burgundy, their duchies, and nearby German principalities. Many languages were spoken in France at the time. He traded in Wine, so he would have had to converse with both suppliers and consumers, who necessarily came from all over what is now France (some of which was ruled by the English Plantagenets in Rashis time) and beyond so he had to know these languages. He demonstrates acute facility with what we call “old French” in his hundreds of renderings of explanations “bla’z” belashon am zu.
When discussing Spain, most of the Jewish population lived in the Northeast of the country, and the language in that area was Catalan, which is still in use today. There were also many Basque speakers in the area of the Pyrenees, where many Jews lived. There were several muslim principalities, as well as Castile, Leon, Andalusia, Galicia (yes, in Spain) and others, all with their own dialects and languages – there was no “Spanish” to know in the 11th/12th century CE. Aroz, Arus, Riz, Rice, all essentially come from the same root, which is the same root in Hebrew, Arabic, Latin, Greek, Italian, French, Spanish, German, Russian, and many other languages. In fact linguists think the root of the word for all of these languages was Tamil, as Rice was first cultivated in the Indian subcontinent.
It is very likely that Rashi’s unclear description may have come from the simple fact that rice cultivation wasn’t introduced into France until over 300 years after Rashi was nifter, though it did make its way to Southern Iberia and Sicily around the time of his life.