TODO: Extract i18n service API into separate module

[jasnell]

https://github.com/covidgreen/covid-green-app/tree/current/services/i18n contains common i18n code to support the application. To help maintain that code and limit the possibility of region-specific variations from cropping up, that should be extracted into its own standalone module.

[ShaunBaker]

As an app developer who desires to fork CGA to create an app for an authority with this proposal I would also need to fork the i18n module, change references in the app to the fork etc in order to continue.

For something that has a small implementation, and is required within the app itself in order for it to work I'm not sure I agree the overheads stated above make this worthwhile. Im not clear on the merit of this proposed change.

cc @jasnell

[jasnell]

Consider this a low priority. Looking across the variations, there is enough similarity between them to warrant separating this out, but I wouldn't consider it a priority.