1414878 - Add LocaleService::SourceLocale

Status: RESOLVED DUPLICATE of bug 1418771

(Core :: Internationalization, enhancement, P3)

Description

[Zibi Braniecki [:zbraniecki][:gandalf]]

In L20n world, we always have a source locale available as a last fallback.

That's different from "defaultLocale" which is the main locale the package is built with and updated for.

For regular en-US build, those two values are the same, but for example for an "it" build, the will be different:

 - defaultLocale is "it" - that's the locale we negotiate down to in case of mismatch (see bug 1391213 for details), that's the locale we call updates for etc.
 - sourceLocale in case of Gecko is always "en-US"

In the future, I believe we will be able to make Gecko not have to hard code the sourceLocale, and just retrieve this information from the build system, but at the moment, we're locked in hardcoded "en-US" both at the build and run time.