The following steps should be sufficient.
wget http://www.carminebenedetto.net/_downloads/asm-intel.lang sudo cp asm-intel.lang /usr/share/gtksourceview-3.0/language-specs/
Please note that the exact folder for copying the .lang file depends on your version. You may have gtksourceview-2.0 instead, or even something else. On my machine, I had both 2.0 and 3.0, and copied the file to each sub language-specs folder language-specs .
Drew noakes
source share