My father has a PowerPoint deck that was initially created by a colleague using a French-language installation of PowerPoint. As a result, many of the slides are spell-checking in French (PPT01).
When I go to Review > Language, "Set Proofing Language" is grayed out unless I have text selected (PPT02). If I have text selected, I can fix the problem, but there are many slides, and I'm looking for a solution that will fix the entire deck at once.
PPT03 shows the Office Language Preferences ... this appears to be set correctly.
My father claims that he frequently experiences the same problem in Word documents. Also, he mailed me the PowerPoint deck, and the same problem manifests on my computer.