I currently have a UK keyboard, and I have configured Ubuntu 16.04 with both UK and Spanish layouts. I generally use the Spanish layout, because it is what I am used to.
Spanish layout: https://commons.wikimedia.org/wiki/File:KB_Spanish.svg
I have a problem though, with the key on the left of the letter Z: With the Spanish layout, I should get the symbol '<', but I get the symbol '\' instead, which is the one from the UK layout.
This is the only key I have a problem with, and it is very annoying. I have no idea where to start looking for an explanation, and it is very difficult to Google it.