There is no hebrew keyboard I know about.
Keyboard definition is a text file (gzipped JSON), so making your own is quite easy.
The other thing is how to install it.
However it is possible to make a hebrew localization package that will take care of installing stuff.
Refer to these posts in this thread:
https://www.mobileread.com/forums/sho...4&postcount=62
https://www.mobileread.com/forums/sho...3&postcount=70