[Translator] added additional conversion for encodings other than utf-8
merged branch benjaminpaap/bugfixes/xliff_encoding (PR #7698)

This PR was squashed before being merged into the 2.1 branch (closes #7698).

Discussion
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[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

Commits
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54bcf5c [Translator] added additional conversion for encodings other than utf-8
[Translation] removed unneeded getter/setter