Background of the issue:
I want to add a new custom language with the language code 'pt'. Currently, we have Portuguese with the standard language WPML provided, which has the language code 'pt-pt'. I want to create a custom language as described and convert all of my 'pt-pt' pages to 'pt' within the WordPress backend and not the database.
Symptoms:
After adding a new custom language, nothing happens.
Questions:
How can I add a new custom language with the language code 'pt'?
Is there something I'm doing wrong?