Add `fallbackLocale`

Apparently the baseLocale option was removed for ember-intl@3, but this seemed like a quite useful option, which prevented users from seeing “missing translation” and instead at least showing e.g. the english version of the thing.

I agree that baseLocale as a way to determine whether translations are missing was not ideal and it’s good that that part got refactored, but I think having such a fallbackLocale option would still be valuable to a lot of projects.

@jasonmit are you open to bringing back such an option?

[jasonmit]

@jacobq thank you for the feedback.

I’m not against bringing back fallback locale where at build time we do a deep merge of the fallback locale and against every locale’s translation object.

I think it would be a relatively easy feature to bring back and could land as part of the current 4.0 beta.

[jacobq]

FWIW, I have a use case for having a fallback (permanent default) locale that I don’t think has been mentioned here yet. I have a number of “locale-less” strings, which are actually IDs like company_1 that should be translated to the same thing in every locale (say, “Google”).

In ember-i18n I was able to provide translation files in js rather than JSON so could just merge those shared values into every translation file, but ember-intl doesn’t seem to offer a way to do this. Now it seems that I either need to duplicate these all over the place (not acceptable), generate the translation files with some other tools (e.g. write a little script to do the merging), or wrap access to the setter for locale (e.g. there is a select element that allows the user to change the language/locale) to ensure that it is always in array form and includes the default locale (perhaps en or perhaps a custom common one, if allowed). This seems like a lot more fuss than necessary to me. Is there another approach that I should be using instead? (e.g. trying to handle this in the missing translation hook)