I do have another version of that macro. Rather than modifying the macro process you know, it instead pre-processes the clipboard with a bit of Applescript – hunts down certain characters/strings and replaces them with paragraph breaks so the text will be in “lines” as the macro you know understand them. In my case, I am sometimes interested in splitting also on commas, semi-colons, or some ad hoc string (‘$$’).
In your case the trick is that is it quite tricky to define syntactically what constitutes a sentence break. Looks like Vincent has given you a jump start.
It’s complicated. There is a whole family of terminal punctuation marks and, depending on the standard your source text follows, sometimes sentences end instead on a quote mark (with terminal punctuation preceding it). Also, terminal punctuation is not always followed by a space or paragraph break, if your text may have footnotes at the ends of sentences. Etc. In short, reliably identifying sentence breaks can be quite involved – with lots of cases and edge cases.