Hi Andras,
Sorry if it took that long before I come back to you, but I tried what you suggested (thank you for the links by the way), but unfortunately I couldn’t find the string in the PO file. However, WPML support helped me with that issu, and I fixed it with their Multilangue Tools plugin.
Here is the link if you would like to take a look, I did the last part at the end of the article:
How do I generate language configuration files using Multilingual Tools? https://wpml.org/documentation/related-projects/wpml-compatibility-test-tools-plugin/
Thank you for your help
Alix