International keyboard settings
To make your keyboard have the accents working for Brazilian Portuguese on Debian-like operating systems in the proper way that Brazilians are used to, you need to add a second Keyboard Layout which uses the English (US, alternative international) language. In some operating systems such as Ubuntu 12 or later, that's all you need to do, but folder others a hack is required to fix the cedilla.
Debian & Pre Ubuntu 12
On versions of Ubuntu before 12, a hack is required to get the cedilla working. Apostrophe then "C" makes a "ć", which doesn't even exist in Portuguese! It should give the c-cedilla (ç). To fix this final problem you need to edit the gtk.immodules (this is in different locations on different distros and versions, sometimes it's in /usr/lib/gtk-2.0/2.10.0/, but if not just find or locate it) configuration file with root privileges. Here's where I found it on my Debian 7 installation:
sudo nano /usr/lib/x86_64-linux-gnu/gtk-2.0/2.10.0/gtk.immodules
Then find the line that configures the cedilla and add an "en" option keeping the items in alphabetical order so it looks like this:
"cedilla" "Cedilla" "gtk20" "/usr/share/locale" "az:ca:co:en:fr:gv:oc:pt:sq:tr:wa"
A restart will be required before the change takes effect, and your cedilla's should be working properly :-)
Linux Mint
On Linux Mint this solution doesn't work because that file doesn't exist, but searching for the word "cedilla" in all files yields the same line in two files which in my case are called /usr/lib/x86_64-linux-gnu/gtk-2.0/2.10.0/immodules.cache and /usr/lib/x86_64-linux-gnu/gtk-3.0/3.0.0/immodules.cache (just search for immodules.cache to find them on your system) and making the change in both of those seems to fix the problem. The only worry is that the file ends in .cache which kind if implies that it could get rebuilt at some point and remove your changes, but it's been working for me so far, and if it does get overwritten I'll add a script to fix it on reboot or something.
To change the flag icon in the keyboard panel applet, do the modifications in the /usr/share/cinnamon/applets/keyboard@cinnamon.org/flags directory.
