Dear Markus @Markus
On the documentation page we have two suggested language plugins - Polylang & Q-Translate XT:
https://laytheme.com/documentation.html#multilanguage
As for SEO - Yoast SEO clashes with Lay Theme so this is not recommended, you may just have to see which suits you and trial if any errors occur.
Sorry for any inconvenience regarding the second point,
Best wishes and thank you for using Lay Theme Markus in 2021
Richard
