# Get a hash of your translations, for quick lookup
%pair_lookup = map { chomp; split(/=/, $_, 2); } <SUBLIST>;
foreach $name (<CUSTLIST>) {
   print NEWCUSTLIST 
         // split the line into words and check if there
         // is a translation for it. If there is, return
         // the translation otherwise return the original
         join(" ", map { (defined $pair_lookup{$_})
                   ? $pair_lookup{$_} : $_; } 
                   split (/ /, $name, 2) );
}