[Translation] added LoggingTranslator.
feature #10887 [Translation] added LoggingTranslator. (aitboudad)

This PR was squashed before being merged into the 2.6-dev branch (closes #10887).

Discussion
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[Translation] added LoggingTranslator.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #3015, #2435
| License       | MIT
| Doc PR       | symfony/symfony-docs/pull/4050

Commits
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b7770bc [Translation] added LoggingTranslator.