A PJ inconsistency?

I just paid attention to this a couple weeks ago after watching FOTR for the umpteen-millionth time (which is a lot, btw) and noticed something I had managed to miss before. At the gate of Moria, the line about the elvish word for friend was taken from Merry as it was in the book, and given to Frodo. This finally clicked with me that it should not be. Frodo is educated, and understands Elvish quite well. He understands Aragorn singing about Beren and Luthien, in the book he speaks with the woodelves as he and Sam are on the road, when he looks at the ring, he doesnt understand, because it is not an elvish language that he knows. Though in Lothlorien some of the dialect confused him, he still understood most of it. Surely, with his education, he would have known the Elvish word for something as common and often used as "friend". Anyone agree?