Default development language

Is your feature request related to a problem? Please describe.
Our client often have separated stores. For this, we only use one code-base. The problem we have is with the translations.

Currently we don't have a dedicated translation file for local development. That means that we're always stuck with our own en-dev.deafult.json. file. The client is then using this file, but since we are also developing with this file, we don't push it with new releases. Only an initial release. Due to this, new translations are not coming through correctly and we had to create our own translation snippet where we can provide a fallback. This is also something that is not really developer friendly, because we are now missing some simple features like autocompletion, error handling and intellisense. Additionally it adds extra lines of code and an extra render.

Describe the solution you'd like
A dedicated locale file (fallback.default.json) for development and can be used as a fallback for our client stores. With this, we can safely push these changes to their stores without overriding their current translations

Locate the code that handles en-dev.deafult.json and locale fallbacks, then review how release files are selected for client stores. Done means a dedicated fallback.default.json is available for development, is used as a fallback, and does not override existing client translations.