[Translation] added logging capability.

| Q             | A
| ------------- | ---
| Doc fix?	 | no
| New docs? | yes(symfony/symfony/pull/10887)
| Applies to | 2.6+
|Fixed tickets |	-
	
you must put double quotes around `%kernel.debug%` since the yaml highlighter uses Yaml 1.0, which doesn't allow `%` to be the first character of a new atom.