New language available for translation notification

**Is your feature request related to a problem? If so, please describe.**
When a user requests a new language, and it is finally accepted and created as a new translation, we don't have any way to contact her/him. The user might get the wrong impression, nobody is taking care of the request, and not returning to the project to contribute.

**Describe the solution you'd like**
A simple automatic notification showing the accepted status of the language into the project will be enough.

Enhancements:

1. It could be optional for the project.
1. It could send a rejection notification too, if for any reason the language is not accepted.

**Describe alternatives you've considered**
I cannot find any alternative. If there is a similar feature right now, please tell me and will test it

**Additional context**
None