This thread is resolved. Here is a description of the problem and solution.
Problem: I am trying to load an iframe in an Elementor HTML block using different src-URLs depending on the language. (example: src="https://...?language=en"). I expected to see the URL using string translation, to be able to change the URL for each language. Instead, I got the URL is not displayed using string translation so I can't translate it.
Solution: In the Advanced Translation Editor the content of the HTML element is not simply copied. Go to Dashboard → WPML → String translation, search for the content of the HTML element, add the translation to it, and mark the Translation is complete box.
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