Redirect using RedirectMatch to language prefix
This is how you can redirect a former indexed path without languagre prefix to a new path with language prefix. In this case i had my old path look like "[domain]/konwledge/[title]" and the new site had a language prefix so the new path should look like "[domain]/en/konwledge/[title]". Add the following in the .htaccess files within the IfModule mod_rewrite.c-tag and modify it.
RedirectMatch 301 ^/knowledge/(.+)$ http://www.zimplicit.se/en/knowledge/$1