<span class="bold">Rayman Colletor</span> was a compilation of every Rayman related stuff that ever came out on PC. It was only available in France, and thus i believe, in french language.
However, it contained more than what was previously featured in the Forever compilation, which we can buy here on GOG. Namely, the full soundtrack was available ingame, there were several minigames, and you could watch a pretty interesting making-of of Rayman 2.

My question here is also a request, and vice-versa.

Why wasn't the Collector version chosen over the Forever to be made available? Was it because of the language being french only (again, i don't remember if that was the case)?
And so, is it realistic to ask for ths particular version to be made available on GOG? :p

Even if it's in French only, it shouldn't make much of a difference for the game itself (there is little text), maybe that can be complicated for save and load functions for non-French-speaking people.
As a French player myself though, I sure would like to see that version available on GOG, especially if it fixes the issues Rayman Forever has. As for players from other countries, GOG could just make a quick reference guide for translations :)