Install tk8.5, if not yet installed:

# apt-get install tk8.5
# update-alternatives --config wish

  Selection    Alternative
          1    /usr/bin/wish8.4
*+        2    /usr/bin/wish-default
          3    /usr/bin/wish8.5</pre>

There are 3 alternatives which provide wish.

Type in the number that corresponds to tk8.5 (in my case was 3) then hit enter.

Change fonts in ~/.gitk to DejaVu Sans Mono.

set mainfont {{DejaVu Sans Mono} 9}
set textfont {{DejaVu Sans Mono} 9}
set uifont {{DejaVu Sans Mono} 9 bold}