On the contrary, if you were the last speaker of a certain language, you would blend in right with everyone else, since no patients will ever benefit from your knowledge of said language. On the other hand, fluency in a second language that is widely used around the schools and residency locations you apply to will be of major help. Like a previous poster mentioned, the grand majority of the students who have taken foreign languages in high school and/or college hardly ever surpass the most basics of the language, unless they majored in it. Out of the hundreds of people I've known who have taken a foreign language, only 3 were able to speak it with acceptable communicational proficiency.