If you want to use code-point ranges, Unicode property classes (see perlunicode) are pretty handy.

sub identify_CJK {
    local $_ = shift;

    return "J" if /\p{Hiragana}|\p{Katakana}/;
    return "K" if /\p{Hangul}/;
    return "C" if /\p{Han}/;
    return "Others";

    # Note that the order matters because Japanese text
    # most likely contains Hanzi (Kanji) characters and
    # so does Korean text (less frequently though).
}
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I think it works in most cases as long as all the texts you want to test are converted to Perl's internal representation of strings (with utf8 flag on).