I think what happens is that your Photoshop is configured to always open JPEG files in Camera Raw. Your Camera Raw is apparently configured to change the resolution of images to 240 ppi, so when you hit Open the resolution of your image changes from whatever it was to 240 ppi.
The image itself hasn't changed. It's still the exact same pixels, but since the ...
One solution could be to save (File > Save As) the PowerPoint slides as image files.
This Microsoft Docs page explains how to edit the Registry to set a higher resolution for the slides. Remember to save a copy of the Registry before editing it.
When you will have saved the slides as images, you can choose whether to use them as slides or to crop the ...
why not generate a text file with all the textual content, run the translation system on that, and then incorporate the translated text into your Keynote, skipping the entire PP-KY-PP mess completely?
Documents which vary in resolution (PPI) will show variations in sizes when moving things between them.
Ensure both documents are set to the same PPI.
In addition, you will want to uncheck Resize Images During Place in the Preferences (General).