On one of my SharePoint 2019 farms a strange error occurred while trying to convert DOCX to PDF using Word Automation Services:

ErrorMessage : The file could not be converted; it may be corrupt or otherwise invalid. Please try opening the file in Microsoft Word, resaving it, and then resubmitting the file for conversion. If this does not resolve the issue, contact your system administrator.
ErrorCode : 131172

Also, in ULS I found this error:
One or more localized components could not be loaded for the specified language. Please check that the required language pack is installed and properly configured.

After spending hours by installing latest Cumulative Updates, Language Pack updates and Windows Updates, I realized that my SharePoint farm is installed in Czech language (without English language pack).

So, I tried to install English language pack, and after that, this error disappeared, and I was finally able to use Word Automation Services.