Well, mastering French is good. Chinese too, Spanish too, Khmer maybe ... etc.
Unfortunately in research, especially if you plan to work with other foreign researchers or if you simply have the good intention to share your work in international symposia; it is necessary (highly recommended) to have a correct level of English. Like really a strict, minimum, correct.
At worst, it would be enough to simply write in one's mother tongue and let someone else / an agency translate into English. But it is not easy because it costs quite expensive to translate a paper / draft that contains let's say, about 7 technical words per line.
So what do we do? Well, we translate by ourselves or we write directly in English.
The result? Nobody understands at all, or much.
If your co-author loses an hour or more each time scratching her/his head trying to decipher what you want to say ... etc, this may be her/his first time with you but most likely her/his last time also.
Suggestion? Strengthen the level of English PhD students / researchers (if possible since the level of license or master).
In the research community, it would be sad to work only with people who only speak your mother tongue, right? And this is also part of the work (and mission, yes) of popularising science in my opinion, especially in this digital age where the information is fairly (too) easy accessible.