Comment 87 for bug 518056

@Leandro: I see that you have Ubuntu 14.04, so this is what you should do: open "Software & Updates", select "Other Software", highlight the cedilla-test item by clicking it and then click the "Edit..." button. In the new window, state utopic as the "Distribution" instead of trusty. I added an attachment which shows the window.

Once that has been changed, you should be able to successfully run

sudo apt-get update

Then you can do

sudo apt-get install xkb-data

or simply

sudo apt-get upgrade