Tcl 10 different chars.

\160\165\164\163 \124\150\145\40\161\165\151\143\153\40\142\162\157\167\156\40\146\157\170\40\152\165\155\160\163\40\157\166\145\162\40\164\150\145\40\154\141\172\171\40\144\157\147

Characters used: , 0, 1, 2, 3, 4, 5, 6, 7, \

Test program:

set code [read stdin]
puts "Characters used: `[join [set ch [lsort -unique [split $code {}]]] {`, `}]`
puts "Number of different characters: [llength $ch]"

Tcl 10 different chars.

\160\165\164\163 \124\150\145\40\161\165\151\143\153\40\142\162\157\167\156\40\146\157\170\40\152\165\155\160\163\40\157\166\145\162\40\164\150\145\40\154\141\172\171\40\144\157\147

Characters used: , 0, 1, 2, 3, 4, 5, 6, 7, \

It's just each part of the command encoded as \ooo sequence. For Tcl, it does not matter if you do such funny things in the command name or in his arguments, in fact the $object configure is very common in Tcl/Tk.
With this technique and eval you could even write every program in Tcl with 10 different bytes :)

Test program:

set code [read stdin]
puts "Characters used: `[join [set ch [lsort -unique [split $code {}]]] {`, `}]`
puts "Number of different characters: [llength $ch]"

Tcl 10 different chars.

\160\165\164\163 \124\150\145\40\161\165\151\143\153\40\142\162\157\167\156\40\146\157\170\40\152\165\155\160\163\40\157\166\145\162\40\164\150\145\40\154\141\172\171\40\144\157\147

Tcl 10 different chars.

\160\165\164\163 \124\150\145\40\161\165\151\143\153\40\142\162\157\167\156\40\146\157\170\40\152\165\155\160\163\40\157\166\145\162\40\164\150\145\40\154\141\172\171\40\144\157\147

Characters used: , 0, 1, 2, 3, 4, 5, 6, 7, \

Test program:

set code [read stdin]
puts "Characters used: `[join [set ch [lsort -unique [split $code {}]]] {`, `}]`
puts "Number of different characters: [llength $ch]"

Tcl 14 different chars.

puts \124\150\145\040\161\165\151\143\153\040\142\162\157\167\156\040\146\157\170\040\152\165\155\160\163\040\157\166\145\162\040\164\150\145\040\154\141\172\171\040\144\157\147

Tcl 10 different chars.

\160\165\164\163 \124\150\145\40\161\165\151\143\153\40\142\162\157\167\156\40\146\157\170\40\152\165\155\160\163\40\157\166\145\162\40\164\150\145\40\154\141\172\171\40\144\157\147