Beherit on "[Plugin: Ceceppa Multilingua] Front page slug"

There is a problem with slug on front page - with Ceceppa I have 2 URLs for one language:

http://domain.tld/en
http://domain.tld/en/

This two links are not good for SEO. I try to configure permalinks to remove first one but with not luck.

https://wordpress.org/plugins/ceceppa-multilingua/