Here is the keyboard layout I use. I think it's very helpful. Of course I do, otherwise I wouldn't have done it! But really, with it

• you don't have to switch keyboard layouts whenever you type in a different language. (not for all the languages in the world, but for most of those that use roman or arabic script)
• you can type arabic script more intuitively, compared with the default arabic layouts - a nightmare even for natives. I use (mostly) the buckwalter transliteration. I did only a couple of changes: the `ayn is 'c', not 'E' and taa marboota is 'ö', not p. So what I do to type an arabic letter is hold the Alt-Gr key and type the roman letter on the keyboard that corresponds to the Arabic character in the transliteration. I type "kitaab" through typing the following keys while holding the Alt-Gr key: "kitAb", and not the following keys: ";ajhf".
• you can type A LOT of additional characters thanks to the dead keys, those shown together with a blue circle in the figure below.

You can use my file, modifying it for your needs if you want. Quick instructions:

• put it in /etc/X11/xkb/symbols/pc/FILE_NAME
• Add a line to /etc/X11/xkb/rules/xfree86.lst specifying the layout name and description
• (If you want to make the new layout the default), edit /etc/X11/XF86Config and modify the InputDevice section for your keyboard to contain the line: Option "XkbLayout" "FILENAME"
• Restart X (Ctrl+Alt+Backspace)

Each box in the figure below shows what are the four characters that each keystroke will produce. The chacaters on the right require holding the Alt-Gr key, and the characters on the top require holding the Shift key. Arabic characters are in red. Dead characters are represented by a light blue cirle where the accent's letter would appear. In addition to being printed above or below letters, these accents can be printed alone by pressing the dead-key twice in a row.