i would:
- use the 2nd dialog as more general (since all metadata is removed, no need to mention comment separately)
- replace "any existing" with "all" or "all embedded" if it fits dialog without breaking sentence (in English) to the second line
follow up Suggestion guess separate post required
Keeping in mind there is another dialog - "Saving in this format will delete some metadata!"
(eg when saving image with XMP metadata into PNG), you my want to list the exact metadata which will be saved/removed from file.