To add a character not provided in a certain Language

Hello 

In the Swiss keyboard the › is lacking. The ‹ is there. 
How do I add a character which is not given to a certain keyboard layout?
It is there on the German one but not on the Swiss one https://de.wikipedia.org/w/index.php?title=Guillemets&action=edit&section=10 Go to macOS.

Thanks