fix: Respect user-defined prefix/suffix when looking for default NS

[alexmchardy]

Fixes #1090 by respecting any custom interpolation.prefix and interpolation.suffix while using localeStructure to see if the default namespace file exists.

Can be tested by changing /examples/simple/next-i18next.config.js to

module.exports = {
  i18n: {
    defaultLocale: 'en',
    locales: ['en', 'de'],
  },
  interpolation: {
    prefix: '%{',
    suffix: '}',
  },
  localeStructure: '%{lng}/%{ns}',
}

Before the change, this config would result in this error:

Error: Default namespace not found at public/locales/%{lng}/%{ns}.json

After the change, the error goes away and interpolations work as expected. (To verify that interpolations work, you need to change /examples/simple/public/locales/en/common.json to use the %{ } prefix and suffix.)

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[devan-huapaya]

Can this be merged? @isaachinman <3

[isaachinman]

Hey @alexmchardy @devan-huapaya – sorry for the delay.

This PR looks great, it just needs test coverage. Thanks!

[devan-huapaya]

No worries @isaachinman I'm just a random who was hoping to use the prefix setting!

I was able to get around the issue by wrapping useTranslation in it's own hook and adding
interpolation: { prefix: <prefix>, suffix: <suffix> } to all hook calls when options were passed in

[alexmchardy]

@isaachinman added a test, hopefully looks good.

cc. @devan-huapaya