Something like (untested):

my %reverse;
while (my ($key, $value) = each %hash) {
    push @{$reverse{$value}}, $key;
}
while (my ($key, $value) = each %reverse) {
    next unless @$value > 1;
    local $" = "' and '";
    print "English strings '@$value' have the same translation ('$key'
+)\n";
}
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