Dynamically load locale messages

[sawyerh]

Ticket

#66

Changes

• Use a dynamic import to load all strings for the selected locale. This simplifies the process of adding a new language — now someone just needs to add the locale code (e.g. es-US) to the locales array, whereas before they'd also have to add an import statement.
• Renamed getLocaleMessages to getMessagesWithFallbacks and moved it to its own file. A few reasons for this:
  (1) Project engineers shouldn't ever need to interact with the getMessagesWithFallbacks logic — it should Just Work. (2) We can now rename i18n/index.ts to i18n/config.ts to make it clearer what the purpose of that file is.

Context for reviewers

I'm pulling this out from the larger App Router migration branch. There's an additional piece that will be in that branch, resulting in a final directory structure looking something like this:

├── i18n
│   ├── config.ts     # Supported locales and formatting options
│   ├── getMessagesWithFallbacks.ts 
│   └── server.ts     # 🆕 next-intl setup logic that can't be imported into client components

@lorenyu We could expand this also to export the safelisted subset of hooks and components

├── i18n
│   ├── config.ts     # Supported locales and formatting options
│   ├── getMessagesWithFallbacks.ts 
│   ├── index.ts      # 🆕 Hooks and components for rendering content
│   └── server.ts     # next-intl setup logic that can't be imported into client components

Testing

[sawyerh]

This was just wrong before

[sawyerh]

I want to rename this file to config.ts but it makes for a confusing diff. I'll rename before merging unless anyone objects.

[sawyerh]

This puts messages on context.loaded.messages, which is available to decorators and stories

[aligg]

🤔 Is this the part you mentioned in the PR description about using a dynamic import to get all the content strings for the specified locale?

Newb question and probably a better way to ask this but does this have any ramifications for like.. the point in build / run time where content strings are brought in?

[sawyerh]

Is this the part you mentioned in the PR description about using a dynamic import to get all the content strings for the specified locale?

Yep, this is the main part of the show. This is the dynamic import.

does this have any ramifications for like.. the point in build / run time where content strings are brought in?

My understanding is that the dynamic import happens at runtime. This avoids statically loading a bunch of content strings that aren't needed, which could impact memory usage.