My question is about the use of " l' " before " on " in certain constructions. It seems to be a pretty advanced style, because I've seen it a few times in novels I've read, but today I picked up " L'aventure des mots français venus d'ailleurs " and have seen very many examples of it in the few pages I've read so far.
What part of the sentences does the " l' " refer to in the following sentences:
" Si l'on sait bien que la langue française est issue du latin, on oublie souvent qu'elle s'est enrichie au cours de sa longue histoire de milliers de mots venus des quatre coins du monde : [liste des langues] "
" Mais ce que l'on oublie très souvent, c'est que le latin n'est pas l'unique source de la langue française, où l'on trouve par milliers des mots venus d'ailleurs. "
The main thing I want to know is what the pronoun is a reference to, but also why it is used and how to know when to use it.
PS. Please excuse my failure to find the cédille! (And, uh, my failure to know what it is called in English...)
ETA: Thank you all so much for your (extremely quick) responses! I suddenly understand why we aren't taught anything about it in school (high school equivalent). And also yay cedilla code things. (Although I'm using Linux, so the HTML is the most useful. In case you were wondering - I do know the Windows ones; just can't seem to find any for Linux.) Thanks!