redirect for http and https VIPs

when HTTP_REQUEST { HTTP::respond 302 Location "https://[HTTP::host][HTTP::uri]" TCP::close }

Would it make more sense to just redirect to "/en/default/welcome" if the URI is empty?

when HTTP_REQUEST {
    if { [HTTP::uri] equals "/" } {
        HTTP::redirect "http://[HTTP::host]/en/default/welcome"
    }
}

Replace "http://" with "https://" in the HTTPS VIP.

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://).

Let's look at this from a flow, based on your original description.

1. user makes a request to "/" and is redirected to "/welcome"
2. user returns with a request to "/welcome" and is redirected to "/en/default/welcome"

At what point do you want users to land on "/welcome" and not redirect?