Can't have non serializable options in i18next in v8

[haggen]

Describe the bug

Now that i18next's options provided are serialized as JSON and sent to the client, it effectively block non serializable values like functions. @zalcode mentioned this in the Next.js 10 issue.

Occurs in next-i18next version

v8.0.0

Steps to reproduce

Provide a function value in i18next options like:

// next-i18next.config.js

module.exports = {
  i18n: ...,
  overloadTranslationOptionHandler: function() {},
};

See an error while compiling:

SerializableError: Error serializing `._nextI18Next.userConfig.overloadTranslationOptionHandler` returned from `getServerSideProps` in "/test".
Reason: `function` cannot be serialized as JSON. Please only return JSON serializable data types.

Expected behaviour

I expected i18next to be configured successfully no matter what types it accepts in its settings.

[isaachinman]

This is specifically mentioned in the docs. You need to set serializeConfig to false and pass the config into appWithTranslation yourself.

Let me know if you have any issues!