fix some issues on examples/app-dir-i18n-routing

[cxa]

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Notifying the following users due to files changed in this PR:

@timneutkens, @ijjk, @shuding, @huozhi, @feedthejim:

examples/app-dir-i18n-routing/middleware.ts

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[milovangudelj]

Was the error catching really necessary?

I was having issues with that code cause Negotiator was returning an asterisk (['*']) from the Negotiator.languages() call, but I solved it by passing it i18n.locales as a parameter like so:

// @ts-ignore locales are readonly
const locales: string[] = i18n.locales;

// Use negotiator and intl-localematcher to get best locale
let languages = new Negotiator({ headers: negotiatorHeaders }).languages(
  locales
);

After this everything went back to working as expected. I mentioned this in #51712.

[cxa]

I don't realize that Negotiator can accept available locales before you mention it. Your method seems more elegant than catching error, just make a PR!

[milovangudelj]

Thanks! Will do 😁

[milovangudelj]

Opened #51786