Unfortunatelly when user changes a language with language switcher while being on that page, WPML changes to a corresponding translated page but without query paramter:
/pl/zamowienie/
which breaks functionality
You can reproduce it by going to our test site:
hidden link
Click Buy on any plan. You will need to register with any data.
After sucessfull registration you'll land on the checkout page with url ending ?pmpro_level=X
Switch a language with Language switcher. You land on polish version of the page without url paramter
Thank you for contacting WPML support. While you are waiting for one of my colleagues to take this ticket and work on it, let me try to provide quick help.
You can preserve these URL arguments by going to WPML → Languages and scrolling to the Language switcher options section. The arguments you want to preserve should be added as a comma-separated list.
