Slug manipulation

You can add rewrite rules to get WP to properly parse the request into query vars it understands.
https://developer.www.ads-software.com/reference/functions/add_rewrite_rule/

This will not cause a post’s URL to change however. For the default post post_type you can define the permastruct you want in the permalink settings screen. This is assuming the language plugin already has a language tag defined and has implemented code to replace the tag with the appropriate language slug.

If not, refer to
https://developer.www.ads-software.com/reference/functions/add_rewrite_tag/
https://developer.www.ads-software.com/reference/hooks/post_link/