There is a very simple way to solve this problem. Especially for this there is a free plugin.
The name of the plugin is Polylang Slug and the author Ulrich Pogson. It’s very simple to use, you only need download the plugin from here, install and activate it.
But this plugin is not being actively developed. Author recommended using Polylang Pro instead as it has this feature and is actively being maintained.
Hope you enjoy this as much as I have.