I have been through a lot of trouble to get c-cedilla (cê-cedilha, in portuguese) as the default for ‘ + c (accute accent + c) on GNOME. In case you don’t know what I am talking about, this is what the character looks like: ç.
Turns out that if I set my language to portuguese, I do get the cedilla by default. The problem is that I really prefer to have my system in english, and with this language I get this character by default: ć.
After reading a bit, I found the gtk-query-immodules-2.0 command, which I have used this way:
$ gtk-query-immodules-2.0 | grep cedilla "/usr/lib/gtk-2.0/2.10.0/immodules/im-cedilla.so" "cedilla" "Cedilla" "gtk20" "/usr/share/locale" "az:ca:co:fr:gv:oc:pt:sq:tr:wa"
This tells me which languages will have the c-cedilla behaviour by default. After some more research I found this link which pointed me to the file /usr/lib/gtk-2.0/2.10.0/immodule-files.d/libgtk2.0-0.immodules. I have edited the cedilla section of this file by adding
to the end of the languages array, like this:
"/usr/lib/gtk-2.0/2.10.0/immodules/im-cedilla.so" "cedilla" "Cedilla" "gtk20" "/usr/share/locale" "az:ca:co:fr:gv:oc:pt:sq:tr:wa:en"
This should be enough. When I restart X I will post the results here.
Update: Yes, it did! Just as a reminder, it is also necessary to choose the international variant of your keyboard. To do that, go to System / Preferences / Keyboard, open the Layouts tab, click on Add and choose your layout (United Kingdom, in my case) and Variation: International (with dead keys).