When using ruby interpolation in externalized strings, they can't be
detected. Which means they will never be presented to be translated.
To mix variables into translations we need to use `sprintf`
instead.
Instead of:
_("Hello #{subject}")
Use:
_("Hello %{subject}) % { subject: 'world' }
* new merge request can be created by sending an email to the specific
email address (similar to creating issues by email)
* for the first iteration, source branch must be specified in the mail
subject, other merge request parameters can not be set yet
* user should enable "Receive notifications about your own activity" in
user settings to receive a notification about created merge request
Part of #32878
