There's nothing like this built-in.
When I was running a service bureau and had to track down rogue fonts fairly
often, we always kept an oddball font or two installed on the PCs. Working on a
copy of the presentation, we'd use Format, Replace fonts to replace MysteryFont
with AlephBeth (a Hebrew font, one that neither we nor our clients ever used).
Then we could manually/visually scan for Hebrew-looking text.
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PPT Frequently Asked Questions
http://www.pptfaq.com/
PPTools add-ins for PowerPoint
http://www.pptools.com/
This should be doable in VBA. Are you on a Mac or PC? What version of
PPT are you using