[Translation] PoFileDumper - PO headers

| Q             | A
| -------------  | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6765 - partially
| License       | MIT
| Doc PR        | 

Po files should not be dumped without a header. It causes a lot of problems, including charset issues.

See #6765 / 1 for more info