Before proceeding further, can you please try the following?
1) Take a full backup of your site and database before proceeding. It is highly advised to try these on a dev or staging site first, so your live site isn't compromised.
2) Deactivate all plugins except WPML and String Translation.
3) Switch to a standard WordPress theme like 2021 or 2024.
4) Go to WPML -> Settings.
5) Look for the section showing translations engines, if you see a few there, try to turn all these off and save the settings.
6) Reload the page and then try enabling these again and save the settings.
7) After that, please go to WPML -> Languages -> Edit Languages and try correct the mapping of the languages and save.
I hope this 'll help fixing the issue. Please let me know your findings and I'll try my best to help you further on the matter.