I'm afraid I can't help you with your vertex problem or with the clean mesh tool, but I'm semi-fluent in french, so I'll take a look at the documentation and see if I can translate the relevant parts for you.

As for your last question, there are a couple things:

First off, I'm assuming that when you say "the program in windows" that you're talking about Notepad (I don't know if it's called something else in french).

Second, it sounds like you're trying to change the files in the default install directory, which is something you robably don't want to do. What you should do is go to your  mods directory and copy the reference data from the mod package into a new folder, which will be the folder for your mod. This way you can turn the mods on and off in the game, without having to replace all the files every time you want to switch mods.

Once you've got the text files in the mod directory, you can use notepad to open and edit them.

I'll check back once I've translated the parts of the documentation you need.