Global t does not handle arrays as defaultNS well

[EvertEt]

🐛 Bug Report

When setting the typescript types through CustomTypeOptions, defaultNS: ['custom']; breaks the type of i18next.t.

To Reproduce

In test/typescript/custom-types, change i18next.d.ts defaultNS: 'custom'; to defaultNS: ['custom']; which should be equivalent (for i18next-react useTranslation.t, it is working)
(Can be found in https://github.com/EvertEt/i18next/tree/error-poc)

Expected behavior

The type/function should work as before (with one or more defaultNS)

Your Environment

• runtime version: Node 20
• i18next version: 23.6.0
• os: Mac

Note

I wonder if
t: TFunction<[DefaultNamespace, ...Exclude<FlatNamespace, DefaultNamespace>[]]>;
should become
t: TFunction<[$FirstNamespace<DefaultNamespace>, ...Exclude<FlatNamespace, $FirstNamespace <DefaultNamespace>>[]]>;
but that might be too simplistic.
The above can be found in https://github.com/EvertEt/i18next/tree/type-fix

[adrai]

Can you create a PR...
@marcalexiei can you review this?

[EvertEt]

I don't have enough time and knowledge to understand why the tests are failing with the above fix, sadly. I've opened a draft.

[EvertEt]

Thanks @adrai and @marcalexiei for the quick fix! We appreciate it.

I've opened a small enhancement to the fix in #2123 for our specific usage.