I created a Dutch hyphenation file for koreader's implementation of coolreader. It's
here.
You could try copying it to the corresponding directory in your coolreader installation. If you can't find the corresponding directory, for instance because it doesn't exist in your installation of coolreader, just put it in the same directory as the other hyphenation pdb-files.
I for one would like to know whether it works for coolreader, too.