Content Review email: Missing text '/contenttypes/ipdffile/name' for 'English'

Description

Steps to reproduce:

1. Install the EPiServer.PdfPreview package.
2. Create a new asset folder.
3. Configure an approval sequence for that folder.
4. Upload a pdf file to that folder.
5. Send a review request / approve review request for the .pdf file.

Expected:
In the content review email, "PDF" should appear next to the pdf file name.

Actual:
The content review email says "[Missing text '/contenttypes/ipdffile/name' for 'English'] ".
Please see attachment for screenshot.