other_function(decode 'latin-1', 'string_literal'))
# and if you want to change a variable
$var = decode('latin-1', $var);

##</code><code>##

do {
   my $var = 'string_literal';
   decode('latin-1', $var);
   other_function($var);
}
# and the other one
decode('latin-1', $var)