[Gelöst] Creating custom language for fluent and plain versions of same language

Background of the issue:
I currently have English and French translations of the website. I want to change both of these to Fluent English and Fluent French and then add a Plain English and Plain French translation, which would be a total of four translations. I can change the name of the default English language to English (Fluent). Once I know how to do this I will be implementing it on all of our websites.

Symptoms:
It only allows me to add English once. It is greyed out when I try to add a custom language of English (Plain).

Questions:
How can I add both Fluent and Plain versions of English and French as separate languages in WPML?