shift Tab acting as meta Tab

[harven]

Hi,

I want to make shift-tab act as meta-Tab.
I tried things like
 (keyboard-translate ?\S-\t ?\M-\t)
without success.

I am using X11 and shift-tab is recognized;
Binding with global-set-key indeed works, e.g.
(global-set-key (kbd "<S-tab>") 'complete-symbol)

If I use this method, however, I have to
rebind S-tab for all modes. A keyboard translation would be better,
but I am unable
to get the character syntax right for the S-tab. Any hint ?