[Translator] added additional conversion for encodings other than utf-8

Added an additional conversion if there is another encoding in the
xlf file present. Values from simple_xml are always utf-8 encoded.
Also added some tests to verify this new behaviour.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT