Need help making Irule more efficient

At a minimum you should probably use an if/elseif structure to avoid unnecessary evaluations. Also, for everything except your single "contains" conditional, you could use a switch context, which is generally faster.

when HTTP_REQUEST {
if { [string tolower [HTTP::uri]] contains "/home/admin-tools/" } {
HTTP::redirect "http://[HTTP::host]/home/"
} else {
switch [string tolower [HTTP::uri]] {
"/" { HTTP::redirect "http://mysite.com/home/" }
"/gb/eng/default.asp" -
"/gb/eng/" { HTTP::redirect "http://[HTTP::host]/en-gb/" }
"/fr/fra/default.asp" -
"/fr/fra/" { HTTP::redirect "http://[HTTP::host]/fr-fr/" }
}
}
}

Given that you have 20 countries to check for, and presumably 40 conditions, it may also make sense to throw everything into a data group for easier management:

Example data group (my_country_datagroup)

"/" := "/home/"

"/gb/eng/default.asp" := "/en-gb/"

"/gb/eng/" := "/en-gb/"

"/fr/fra/default.asp" := "/fr-fr/"

"/fr/fra/" := "/fr-fr/"

Example iRule:

when HTTP_REQUEST {

if { [string tolower [HTTP::uri]] contains "/home/admin-tools/" } {

HTTP::redirect "http://[HTTP::host]/home/"

} else {

if { [class match [string tolower [HTTP::uri]] equals my_country_datagroup] } {

HTTP::redirect "http://[HTTP::host][class match -value [string tolower [HTTP::uri]] equals my_country_datagroup]"

}

}

}