redirect for http and https VIPs

Try this:

when HTTP_REQUEST {
    switch [string tolower [HTTP::uri]] {
        "/" -
        "/welcome" {
            HTTP::redirect "http://[HTTP::host]/en/default/welcome"
        }
    }
}

Assuming you're offloading the SSL for your HTTPS VIP traffic, the iRule should be the same except for the redirect scheme value (https:// vs. http://).