[Issue #3078] cleanup translation related code

[doug-s-nava]

Summary

Fixes #3078

Time to review: 30 mins

Changes proposed

Context for reviewers

When testing translation behavior, it was difficult to track down why the Spanish version of the site was not loading. In the end, it was a matter of us manually setting "en" as the locale in a number of places unnecessarily. Since getMessagesWithFallbacks handles filling any missing messages in with English, so there isn't a need to manually set
the request locale to "en".

This change updates the entire app to support dynamically set locales.

It also:

• updates outdated next intl set locale methods (unstable_setRequestLocale is now stable, see feat: Mark setRequestLocale as stable amannn/next-intl#1437)
• includes a couple of quality of life improvements related to translation code

Test steps

1. add some spanish messages for local testing. Add the following to the spanish messages file:

export const messages = {
  ErrorPages: {
    page_not_found: {
      title: "No pagina nunca",
    },
  },
  Subscribe: {
    form: {
      name: "Nombre Primero",
      lastName: "Nombre Ultimo",
    },
  },
};

2. visit http://localhost:3000/es/subscribe
3. VERIFY: the spanish input titles added in step one appear
4. visit http://localhost:3000/es/subscrdfafdfibe
5. VERIFY: the spanish heading added in step one appear

Additional information

Screenshots, GIF demos, code examples or output to help show the changes working as expected.

[doug-s-nava]

see https://next-intl-docs.vercel.app/docs/usage/configuration - using a request.ts file, config will get picked up automatically. Not sure why this was in server.ts instead

[doug-s-nava]

this is a bit unfortunate, but seems to be the best way to deal with testing a top level page that takes params from the Next system

[acouch]

Was there a reason for renaming this?

[doug-s-nava]

yeah, you can see my note in the config file - basically next intl will automatically pick up a file called request, whereas ours was called server and we had to pass a path to it to get it to work. Simplifies things slightly and makes use of built in behavior

[doug-s-nava]

had to make this change to get tests to work, but this wasn't doing anything anyway

[doug-s-nava]

moved this over from the getMessagesWithFallbacks code. Not a necessary change but just made more sense to me to do the locale default logic as high up in the call stack as possible

[acouch]

🎉 🇪🇸 🚀 !