I just found this thread after experiencing the same problem myself and confirm that Christine's helpful tip above (right click and 'Edit data') works a treat. Thank you!

This is a known 'feature' and was detailed in the release notes (I think). Certainly, this is the only way to get the translated text in Excel objects to be displayed. Although irritating, is means going through the PPT file and checking every slide, which helps to capture frequent text box sizing issues caused by different numbers of words/characters when translating to another language.

[edit] I've just finished one of these files - On saving target file, Studio displayed an error message warning of embedded Excel objects and reminding me to refresh the objects in the target file.