一、编码范围
1. GBK (GB2312/GB18030)
x00-xff GBK双字节编码范围
x20-x7f ASCII
xa1-xff 中文
x80-xff 中文

2. UTF-8 (Unicode)
u4e00-u9fa5 (中文)
x3130-x318F (韩文)
xAC00-xD7A3 (韩文)
u0800-u4e00 (日文)
ps: 韩文是大于[u9fa5]的字符

正则例子:
preg_replace("/([x80-xff])/","",$str);
preg_replace("/([u4e00-u9fa5])/","",$str);

二、代码例子

//判断内容里有没有中文-GBK (PHP)
function check_is_chinese($s){
    return preg_match('/[x80-xff]./', $s);
}
//获取字符串长度-GBK (PHP)
function gb_strlen($str){
    $count = 0;
    for($i=0; $i 127) {
            $count++;
            if($value >= 192 && $value <= 223) $i++;
            elseif($value >= 224 && $value <= 239) $i = $i + 2;
            elseif($value >= 240 && $value <= 247) $i = $i + 3;
            else die('Not a UTF-8 compatible string');
        }
        $count++;
    }
    return $count;
}

//截取字符串-UTF8(PHP)
function utf8_substr($str,$position,$length){
    $start_position = strlen($str);
    $start_byte = 0;
    $end_position = strlen($str);
    $count = 0;
    for($i = 0; $i < strlen($str); $i++){
        if($count >= $position && $start_position > $i){
            $start_position = $i;
            $start_byte = $count;
        }
        if(($count-$start_byte)>=$length) {
            $end_position = $i;
            break;
        }  
        $value = ord($str[$i]);
        if($value > 127){
            $count++;
            if($value >= 192 && $value <= 223) $i++;
            elseif($value >= 224 && $value <= 239) $i = $i + 2;
            elseif($value >= 240 && $value <= 247) $i = $i + 3;
            else die('Not a UTF-8 compatible string');
        }
        $count++;
    }
    return(substr($str,$start_position,$end_position-$start_position));
}

//字符串长度统计-UTF8 [中文3个字节，俄文、韩文占2个字节，字母占1个字节] (Ruby)
def utf8_string_length(str)
    temp = CGI::unescape(str)
    i = 0;
    j = 0;
    temp.length.times{|t|
        if temp < 127
            i += 1
        elseif temp >= 127 and temp < 224
            j += 1
            if 0 == (j % 2)
                i += 2
                j = 0
            end
        else
            j += 1
            if 0 == (j % 3)
                i +=2
                j = 0
            end
        end
    }
    return i
}

//判断是否是含有韩文-UTF-8 (javascript)
function checkKoreaChar(str) {
    for(i=0; i 0x3130 && str.charCodeAt(i) < 0x318F) || (str.charCodeAt(i) >= 0xAC00 && str.charCodeAt(i) <= 0xD7A3))) {
            return true;
        }
    }
    return false;
}

//判断是否有中文字符-GBK (javascript)
function check_chinese_char(s){
    return (s.length != s.replace(/[^x00-xff]/g,"**").length);
}