We do not have full i18n support. The locale stuff in the base system
is not finished (I know, I'm late...)

Qt has its own locale system, so hebrew should work just fine in all
Qt and KDE applications (including right-to-left text).

Gnome and gtk also have some support. 

Vim supports more or less every script including hebrew.

I don't know if there's any issue with input, I'm not familiar with
hebrew, and I've only been working with japanese input.

There might be some tweak to help OpenOffice. Does OpenOffice support
hebrew on some platforms ? If it does, it might make sense to try to
figure out the configuration differences.