Hi Benjamin,
Thank you for the response. Even if this working mechanism is technically right, I don’t think it’s the preferred one for best results. I believe this plugin should single-handedly configure the sitemaps as including/allowing these information and signal the content’s lang without letting google to make the all searches among contents and checks it by itself. It would be much more efficient way to do this. I also tried to add this with php codes to “mimic” the polylang behavior and checked the wp logs and realized that somehow Seopress didn’t allow to show these info inside xml sitemaps. So, I believe this is just its working mechanism and cannot be changed but I suggest developers should add this feature later on.
Thanks again for your reply,
Have a nice day.