WPML provides a reset feature that deletes WPML tables from the site’s database and deactivates the plugin.
The reset action does not delete translated images, translated posts, and translated taxonomies. It only affects translation and language information that WPML associates with each content type. If needed, you can delete existing translations for removed secondary languages.
Please note that all translations you have sent to remote translation services will be lost if you reset WPML’s data. They cannot be recovered later.
To reset WPML, go to WPML → Support and click the Troubleshooting link. In the Reset section of the Troubleshooting page select the I am about to reset all translation and language data checkbox and click the Reset and deactivate WPML button.