One way I think this could work is if the WordPress site is using a multi-site setup. Each subsite can connect to its own Discourse instance. On a single-site WordPress setup, it is only possible to connect to a single Discourse forum.
Another possible approach would be to use a single Discourse forum, and give each locale its own category. You could log users into the correct category from WordPress.
With SSO it is now possible to set the user’s locale. The WordPress plugin has a filter that can be used for adding the locale to the SSO payload.