fixed translator locale when dealing with sub-requests

| Q             | A
| ------------- | ---
| Bug fix?      | yes, kinda
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This fixes the (edge) case where the locale of a sub-requests is different from the locale of the master request. The listener synchronizes the translator locale with the one from the request.