User navigator local in the MERN stack

I'm trying to build a web application with support in 2 languages, with react-Intl .

The problem is that when I initial load from the server I do not have the user's browser language so I can not determine which language to display. I want to check it out in IntlReducerstate but I do not have access to Navigator of course because it's a load from the server.

What do you suggest?