WPML’s String Translation only stores MO files on one server, so requests handled by other servers do not translate strings. To synchronize translation files across servers, you need to enable a custom mode.
To sync translation files across all servers, add the following to your wp-config file:
define( 'WPML_ST_SYNC_TRANSLATION_FILES', true );
This synchronization mode adds another layer of logic that may affect your site’s performance. We recommend using it only if required.