The source file is treated as iso-latin-1 since you didn't tell Perl otherwise. So you end up seeing the result of

decode 'UTF-8',                # Your terminal
    encode 'UTF-8',            # binmode
        decode 'iso-latin-1',  # Perl reading the source. \ MISMATCH
            encode 'UTF-8',    # Your editor              /
                "Çirçös"
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By telling Perl the source is UTF-8,

decode 'UTF-8',                # Your terminal
    encode 'UTF-8',            # binmode
        decode 'UTF-8',        # Perl reading the source
            encode 'UTF-8',    # Your editor
                "Çirçös"
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You want:

#!/usr/bin/perl
use utf8;
use open ':std', ':locale';
print "Çirçös\n";
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See utf8, open