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While waiting for one of my colleagues to help with this ticket, and based on what you've described, allow me to walk you through some initial debugging steps.
From your screenshot it seems that this description is coming from an option page in Rank Math right?
- First, make sure to have "WPML SEO" installed as it will improve the compatibility between WPML and Rank Math.
- Go to "WPML > String Translation" and search for that description and translate it.
- If you can't find it, stay on "WPML > String Translation" and scroll to the end of the page and click the link "Translate text in admin screens" at the bottom left.
- On the next page, search for the description, select it (checkbox at the left) and click on "Add to String Translation".
- Go back to "WPML > String Translation" to translate it.
In short:
- Go to "WPML > Support > Debug Information" (link)
- Copy the Debug Information from there.
- Find the private field I activated and paste that information.