Hello,
All DOCX documents use the same internal XML files. It doesn't matter the language/region version of MS Word you are using. We have MS Word versions of many languages and regions: english, german, spanish, french, asian languages, italian... and all of them work correctly with phpdocx.
We recommend you run the samples included in the package: LayoutAndGeneral/addProperties folder and check the output.
Please note that your code has a PHP error:
'subject' => 'Subject,
This line should be:
'subject' => 'Subject',
If you send to contact[at]phpdocx.com the DOCX output after running your code (and the DOCX template if you are using any), we'll check it. Maybe you need to set a custom property for the DOCX you are using?
Regards.