Language header based on country code.

language-header.vcl

sub vcl_recv {
  # Set a X-Language header to spanish is the client is from a spanish speaking country
  if (req.http.section-io-geo-country ~ "^(AR|BO|CL|CO|CR|CU|DO|EC|SV|GQ|GT|HN|MX|NI|PA|PY|PE|ES|UY|VE)$") {
    set req.http.X-Language = "Spanish";
  } else {
    set req.http.X-Language = "English";
  }
}

sub vcl_hash {
  hash_data(req.http.X-Language);
}