Translation ZIP of single XML file can not be imported

Steps to reproduce:

1. Create a Translation ZIP file with all pages in one single XML file

2. "Translate" this file and ZIP it

3. Import the translated file

Expected result:

• Translation is imported and content is translated

Actual result:

• The message "Translation descriptor file is missing." is displayed

Workaround:

• Do not ZIP the file, but directly import the XML