custom keyboard layout

[arno2]

I need a custom keyboard layout
(the Germany keyboard <de-de>
+ all transcription letters for Arabic and Hebrew <ā Ā ḇ Ḇ č Č ḍ Ḍ ḏ Ḏ ...ʾ ʿ>
+ letters needed in Turkish <ҫ Ҫ ş Ş ğ Ğ ı İ>
using AltGr and Shift-AltGr for the extra letters.
BTW, the German keyboard includes French, Italian, Spanish letters via dead keys)
I want to do it on live Ubuntu from a USB stick in persitent mode.
If it is impossible, I want do use it in installed Ubuntu.