From: AES on
I don't have PowerPoint on my MacBook. When I've dbl-clicked on .ppt
files received from someone else, in the past I've gotten a message
saying that an app called e1.strings was going to be opened for the
first time.

I know how to use Get Info to make Keynote the default app for these
..ppt files, and have now done so. But just for my personal education,
what is (or was) e1.strings?