Support multiple languages (i18n) for the text message copy

[greggles]

TL;DR

It would be nice to be able to send text messages to people in their primary language. It looks like some work on this happened in #1107 but from the API docs I don't see how a consumer would use that.

Design

Proposal

• The admin interface should allow for specifying the accepted languages and associated copy.
• The API should have a parameter for choosing one of those languages (and error if an unconfigured language is requested)

Alternatives considered

I think an API consumer could get a code and then do the localization locally and then send the message, but I believe the long-expires URL token is not returned in the API response (maybe I missed that in my read of the API).

Resources
n/a

Additional information
n/a

[sethvargo]

The changes made as part of #1352 will enable this. The feature isn't language-specific, but you'll be able to define multiple templates. You could do different languages or different variations of messages on the same language.

/cc @whaught

[mikehelmick]

@sethvargo beat me to that by seconds...

[sethvargo]

Duplicate of #1320

[greggles]

As usual, thanks so much for the quick response!