How about if you show us just enough code to demonstrate the problem -- i.e. assign characters to a scalar, apply substr to the scalar, print the result in some way -- and show us what you actually get as a result. (In the little snippet you showed, there should be a comma between the 0 and the 2.)

For example, this should do what you intended:

my $target = join("", map {chr()} ( 0x5434, 0x9547, 0x5b87 ));

my $part = substr( $target, 0, 2 );

print " length of target = ", length($target);
print "\n length of substr = ", length( $part );
print "\n $target\n $part\n";
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The length function should return the character counts (3 for $target, 2 for $part). If you are using a utf8-aware display window, you should see the two strings in Chinese characters (or redirect to a file, and view that in a utf8-capable display tool, like a browser).

If you get something different, tell us what OS and perl version you have, and be specific about what you actually got.