#It gives weird result:
$text =~ s/\\u(.{4})/pack('u', $1)/ge;
$text =~ s/\\u(.{4})/pack('U', $1)/ge;

#Says, nonnumeric argument:
$text =~ s/\\u(.{4})/pack('u', "0x$1")/ge;
$text =~ s/\\u(.{4})/pack('U', "0x$1")/ge;
$text =~ s/\\u(.{4})/chr("0x$1")/ge;

#Just stays as a changed string (\x{00e9}, \x{00f3}, \x{00e1},
#or with \0x{....}), doesn't interpolate:
$text =~ s/\\u(.{4})/\\x{$1}/g;
$text =~ s/\\u(.{4})/\\0x{$1}/g;

#does not change anything:
use Text::Unidecode;
$text =~ s/\\u(.{4})/unidecode($1)/ge;