Is any startup ever "done" in just one language? Everwhere I've been there are a half a dozen. Why not just wait to see what Arc ends up doing really well out

Is any startup ever "done" in just one language? Everwhere I've been there are a half a dozen. Why not just wait to see what Arc ends up doing really well out of the box and then considering it for that and leave the things it doesn't handle to something else?