How to fix erratic keyboard language switching on Mac with multiple keyboards and languages?

I have a macbook pro with spanish keyboard and I use a british external keyboard. With this configuration and 3 languages (ES, US INT, UK), I need to change between keyboard languages often, using the left inferior key with the FN and the globe. My experience is quite negative as the functionality is quite erratic. Sometimes I need to press the key several times in order to change the language. Other times it changes fast and well. It looks like it needs some time to start as a cold engine. Does this happen only in my computer or is it a general MacOS problem?

[Re-Titled by Moderator]

Original Title: Problems changing keyboard language