Have you looked at various subtitle sites like opensubtitles .org? I've thought that one specializes in films, but there may be other media I haven't noticed.
This will sound naïve, but is it common for PDF books to offer multiple language files? Also, surprised that the ad didn't make mention availability – unless there is none.
Is there a toll-free number on the sales site, so you could call for assistance? Or, at least the book's publishing house?
Or, is it a self-published book where author contact info is harder to find? Sorry I can't help more (if this was any, lol).