There are some WP User Manager addons that have strings used in the frontend of the site that will also need to be translated with WPML.
For example, the WPUM Delete Account addon adds a new account settings page called ‘Delete Account’:
To translate the strings in the Delete Account addon, you will need to WPML String Translation addon:
Then go to WPML > Theme and plugin localization, scroll down to ‘Plugins’ and select the ‘WPUM Delete Account’ plugin and then click Scan selected plugins for strings.
Once WPML has scanned the strings, they will be available to translate in WPML > String Translation under the ‘wpum-delete-account’ domain.