Linguist is not an interpreter, the same for Russian: linguist is лингвист, филолог deals with philology and not linguistics and interpreter is переводчик.

As for бабушка, I didn't get from your post what is wrong with the word. Speaking about grandmums with friends, I say бабушка, with relatives (about my grandmums) - бабуля (but that's not a general practice with бабуля, I think it's rather rare).