[Feature Request] Replace `app/utils/intl/missing-message.js` with hook

How about replacing the magic file at app/utils/intl/missing-message.js with a hook on the service?

Something like this:

// ember-intl service
// …
missingTranslation(locale, key, options = {}) {
  return `Missing translation for ${key} in ${locale}`;
}

// …

That hook could be used both to modify the returned message, e.g. by hooking up a fallback message in a specific locale, or used to notify some backend system about the missing translation.

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The missing-message magic file works, but it’s an unorthodox way of doing it, and it causes some confusion, for example https://github.com/ember-intl/ember-intl/issues/627

[sandstrom]

@jasonmit I don’t mean to rush you!

I just wanted to connect the issues @jacobq mentioned in the issue he opened back to this one, since I think the hooks discussed here could give him adjustability around how errors are handled, and instead of having to choose between fail-hard vs. soft-fail, a hook would let the user choose whether to return a value or raise depending on preference/environment/etc.

[sandstrom]

Let’s continue the discussion in https://github.com/ember-intl/ember-intl/issues/1299#issuecomment-629107847 here.

I think having hooks that could throw errors, return a custom string, or do any work really, would very useful.

The default behaviour could be to raise exceptions, for example for missing translations, missing args, etc. But hook would allow customization. That way one can choose to alter behaviour depending on environment, return a string + notify Sentry/TrackJS/Bugsnag, send notification to backend, etc.

Our upgrade to ember-intl has been smooth overall, but one issue that has cropped up several times is production crashes on missing translations or arguments (e.g. unresolved promise). Obviously those are bugs in our code, but with the old lib we’d just render fallback strings or error messages and our app would still be useful (+ send notification behind the scenes). Now everything just crashes.

Hooks where we could customize behaviour upon failure would be very useful!

Thanks again for all your awesome work on this addon! 🏅

@jasonmit let me know what you think!

cc @jacobq