Regarding ly snippets, there are 2 possibilities:
1) PNGs and code snippets from the English docs are used for the
translated docs through symlinks. The main advantage is that translated
docs don't take too much time to make and don't take too much disk space
on lilypond.org.
2) ly snippets in translated docs are totally independent from ly
snippets from untranslated docs. This has 2 advantages: it is easier to
write the makefiles and it makes the snippets translatable, which is
nicer for the end-user (texts and maybe pitch names could be
translated).
I prefer #2 over #1. Maybe we could ask end users on lilypond-user-fr to
give their preference?