Frenchman here. French companies and organization, in my experience actually really like the English language (at OVH for example, most official docs are in English), but I do think it makes sense for a government funded by people who speak mostly French (ie the French taxpayers) to do stuff in French, the language most of its citizens will be most familiar with.

Putting stuff in English will tend to exclude the less educated, or people who struggle to learn foreign languages.

EDIT: and actually, from looking at the README of https://github.com/cloud-gouv/securix

> Ce README est en français mais le reste du code, les issuers et les PR sont en anglais.

The README is in French but the rest of the code, the issues (they wrote issuers, but that is a typo I suspect) and the PRs are in English.

So. :P