Is it safe to use reactI18nextModule on the server?

[testerez]

I didn't find much documentation about reactI18nextModule and I was wondering if it's safe to use on the server considering that we could be rendering multiple pages for different languages at the same time.

Would you mind explaining how the instance would be tied to a specific request?

[jamuhl]

react-i18next does not solve the problem of having an i18n instance per request fixed to the language of that user...this is done by eg. https://github.com/i18next/i18next-express-middleware (same exists for koa and others)

also checkout the samples for next and razzle:
https://github.com/i18next/react-i18next/blob/master/example/nextjs/server.js#L8
https://github.com/i18next/react-i18next/blob/master/example/razzle-ssr/src/server.js#L11

[testerez]

I guess reactI18nextModule is storing the instance in some kind of global variable so it can't be used with SSR, right?

[jamuhl]

the reactI18nextModule is just taking the i18next instance (i18next itself) https://github.com/i18next/react-i18next/blob/master/src/context.js#L29 (basically the global i18next instance - not the one from request)

eg. for next.js:

we use initialProps: https://github.com/i18next/react-i18next/blob/master/src/context.js#L29
and get that from req: https://github.com/i18next/react-i18next/blob/master/example/nextjs/i18n.js#L38

for razzle:

has entry point for server using the one on request: https://github.com/i18next/react-i18next/blob/master/example/razzle-ssr/src/server.js#L35
and client: https://github.com/i18next/react-i18next/blob/master/example/razzle-ssr/src/client.js#L11

[testerez]

Ok I see, it's in fact a global: https://github.com/i18next/react-i18next/blob/master/src/context.js#L11
So even if I pass the right instance, if another request starts before the current one finishes, the instance in use will be replaced. If both requests have different languages it could be an issue.
So my conclusion is: For SSR use the provider not reactI18nextModule

If what I say is correct it could make sense to make it clear in the documentation.

[jamuhl]

think that makes sense...basically it's always about "injecting" the req.i18n so ssr case is rather tight coupled to i18next-express/koa-middleware

[jamuhl]

docs updated: https://react.i18next.com/misc/universal-rendering.html#samples