[de] Convert windows-1252 files to UTF-8

[LeMyst]

Description
Some DE files are encoded in "windows-1252" charset instead of UTF-8.
I think it's a mistake and after a quick research I didn't find a closed issue about this or any logic why these files are in a different encoding.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

Out of scope of this PR.. How can we check if all files are encoded properly? Can we add an auto-review test for that?

[kenjis]

@paulbalandan

$ find Language/de/ -type f -exec file --mime {} \; | grep -v charset=utf-8 | grep -v charset=us-ascii
Language/de//Files.php: text/x-php; charset=iso-8859-1
Language/de//Test.php: text/x-php; charset=iso-8859-1
Language/de//Publisher.php: text/x-php; charset=iso-8859-1

[MGatner]

I'm approving this but I have no idea 🤷‍♂️

[kenjis]

I cannot read de, but every file encoding is UTF-8.

[paulbalandan]

Thank you, @LeMyst