Unfortunately here wouldn't be the best place to get this one resolved as the MultilingualPress team will be better able to assist. In order for this to be possible it would need to be one of the features of their plugin since they would be handling the translations.
I would recommend getting in touch with their support team below. hidden link
In a case like this it would definitely need custom coding which is out of the scope of our support forum.
The main issue is that with WP multisite installed the databases for the sites aren't shared and they're self contained. This means that in order to sync any information custom database queries will need to be used.
Unfortunately there isn't much I can provide here in terms of assistance given the specific issue.