I have just installed Ubuntu 14.04 on my laptop and had a hard time figuring  out why the very common cedilla letter in Brazilian Portuguese was not working. Instead this letter was showing up: ć.

After digging online on many different places. This seem to be an old issue that is recurring on every Ubuntu version. The solution for me was use the English (US, alternative international) keyboard and add the following couple lines to my /etc/environment file:
GTK_IM_MODULE=cedilla
QT_IM_MODULE=cedilla

And voilá! Now the very popular Brazilian letter is back normal so you can write: criança, coroação, combinação, importação, adição and hundreds of words with Ç instead of ć