Redirect root page to specific store (language) view

Question

We setup a Magento 2 Shop with 3 languages: Www.domain.com/de_ch/ Www.domain.com/fr_ch/ Www.domain.com/en_ch/

Where de_ch is the default language. The problem now is, that we get duplicate content for www.domain.com and www.domain.com/de_ch/

How can we permanently redirect www.domain.com to www.domain.com/de_ch/ ?

Or is there another approach to omit the duplicate pages for search engines?

Thanks Aldo