Language Naming

I'm attempting to come up with a family tree of Languages for my Fictional
world, and it occurs to me that I'm not nearly as sure about the general
"convention" of naming languages.  From what I can tell many languages are
named after the country in which they originated, English : England, Welsh :
Wales, Spanish : Spain, Italian : Italy, Russian : Russia, etc., etc.  Now I
don't want a complete list of the names of each natlang known to man.  What
I'd like to know is, "What are the most common ways for speakers of language
X to name it?"  After the Country of origination is easy, and seemingly the
popular method; but, what about Latin?  Did the Romans call it Latin (or
some inflected version thereof) or did they call it something else?  What
about Swahili?  Is swahili the name of some long forgotten country, or did
they just decide one day to call their language Swahili?  What is the
precedent for Semitic languages?  Is Arabic an English invention, or do
arabs actual pronounce something approaching Arabic when they name their
language?  Well, by now I hope my point and question has been successfully
communicated, and I'm sure a lot of you guys can give general rules about
how to name languages.  Now I just gotta find that multifractal based
earthlike-planet generator algorithm I've got laying around somewhere.....
:)