Is this really necessary? Shouldn't it fallback automatically?

If this is not the case, we may move this check down here and fallback to defaultLocale if undefined.

locale is always there (except maybe for nextjs prior to when locale was added)

I don't really want to the throw Error in there. I feel it's enough with the ??.

Second for the sake of the simple example I don't really want to require/import the next-i18next.config.js to get the fallback. At least not yet, cause it wasn't working in olders version without the localePath trick. I mean all those next-i18next, nextjs legacy but supported. At least If I remember well.

That said a more advanced example should be great.

One that typechecks the keys and handle properly localePath in all scenarios (getStatic, getServer, app and csr pages + monorepo), but for that the example will look a bit like bryanprimus/layout-reproduce-i18next#1. Which will make the simple example less simple.

So for now, I'm just focusing on whatever help me for publishing in a safe way.

Doing so I saw a lot more to do in the codebase and those little might not be necessary anymore once I've cleaned'up. (not sure I can but let's hope)

I mean in the library code, not in the example code... check the links in my previous comment.

tldr; I would remove the ?? 'en' part, as this should already work and if not, we'll adapt the library code to automatically fallback.

Ah yes. To be sure we're talking about the same

Here nextjs type the locale as string | undefined, and I want it as string.

Even if we would accept an undefined as first parameter to serverSideTranslations and do the job there, I feel would worsen the signature (I mean having optional as first param is not living well, ie myFunction(undefined, undefined, {param: 1})

I don't feel neither than nextjs is at fault here. It's good that the developer handles the fallback. I mean in how next-i18next works right now. And mysefl I tend to create my own function (that will deal with more)

ok

That is the part that I want to merge into the peer-deps change and new publishing. It will help me cover edge cases