ok, I thought it was possible, the most important for me is to customize the registration form of wpForo, I saw that there is an addon but it pays, I do not I do not have money, I just want to add a field "first name" and a field "name", that's all, can you help me find a custom code to add in functions.php? Then, by default, the first name and the name appear on the forum, not the pseudo.

If you use UM, then the registration and login pages should also used by UM. UM has all options to create a custom registration form. Just create that form and change wpForo Registration page URL to UM page URL using the according option in Dashboard > Forums > Settings > members admin page.

You can find all necessary instructions here:

https://docs.ultimatemember.com/article/87-adding-a-registration-form

since it is not possible to integrate ultimate member at 100%, I do not want to use it anymore (I just delete it). Now I have to customize the wpForo registration form

I see another problem:

I update the translation of the FR file (french) of wpForo (po file), it lacks translation strings in your .pot file, so I can not translate it entirely

here are the English translation channels that I can not translate into French (see attached file) , it is not translated, yet in my .po file (edit with poedit) everything is translated into French at 100 %