added logging  to translator.
feature #4050 [Translation] added logging capability. (aitboudad)

This PR was submitted for the master branch but it was merged into the 2.6 branch instead (closes #4050).

Discussion
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[Translation] added logging capability.

| Q             | A
| ------------- | ---
| Doc fix?	 | no
| New docs? | yes(symfony/symfony/pull/10887)
| Applies to | 2.6+
|Fixed tickets |	-

Commits
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e8e50fa added logging  to translator.