I created a widget language switcher to be able to insert it as a shortcode in my header with horizontal list, and I would like to add a vertical bar between the two languages.
Can you please help me out?
Thanks hidden link
Both solutions require custom coding and this custom change falls outside of our scope as support, that's why I also gave you a link where you can find our certified partners who can develop custom solutions like the one you desire: http://wpml.org/documentation/support/wpml-contractors/. They will be able to work on custom development with you.
Anyhow, try to add the following code to your Appearance > Customize > Additional CSS
This will give a separator as you have only two languages.