I am new here. I am looking for a bi-directional editor that works with LaTeX system and supports Unicode. I need it in order to write Hebrew, Arabic, etc.
Emacs with AUCTeX supports utf8 and bidirectional text.
Further details can be found in this answer: https://tex.stackexchange.com/a/356/7880
Here is a full guide on getting Arabic text to work on linux, including both vim and emacs: From the sounds of it you need an Arabic bitmap font installed: http://projects.arabeyes.org/download/documents/howto/arabic-howto-en/
You might want to have a look at http://www.emacswiki.org/emacs/DisplayEngineForArabic which describes an ongoing project to have full support for arabic.
There are directions here as well, but they seem somewhat out of date and involve compiling yourself: http://www.m17n.org/emacs-bidi/emacs-bidi.html There are more details and screenshots at the older version of the site: http://www.m17n.org/emacs-bidi/emacs-bidi-old.html
If you have trouble with left to right text this page had details on it: http://www.emacswiki.org/emacs/SupportBiDi
Finally a page on bidirectional fonts: http://www.gnu.org/software/emacs/windows/Fonts-and-text-translation.html