Every once in a while I get a PDF file (that usually (but not always) has a usable text layer) containing a research paper in English. I need to determine the variant of English (British vs. American would do). What I do now is manually searching for occurrences of words that make a difference: behaviour, behavior, color, colour, analyse, analyze, etc. This is unreliable, but better than nothing, and moreover, I can't search for all the differences between the two languages. Are you aware of any Web app (or standalone app) that would do this automatically? If so, how about trying it out on https://www.doi.org/10.4153/CJM-1961-007-5 ?