Ok done, thanks to
Halja !
My problem was mainly my french client.
Code:
<Bindings>
<Layer name="SI_KEYBINDINGS_LAYER_GENERAL">
<Category name="SI_KEYBINDINGS_CATEGORY_USER_INTERFACE">
<Action name="MUTENPC">
<Down>mute()</Down>
</Action>
<Action name="UNMUTENPC">
<Down>unmu()</Down>
</Action>
</Category>
</Layer>
</Bindings>
Great, I share this now xD