function language_change(){

    var item_1 = ["", "Exam 1", "Exam 2", "Exam 3"];

    var item_2 = ["", "COREOS", "INTEOS", "LEADOS"];

    var selectItem = $("#sel_language").val();

    var changeItem;

    if(selectItem == "Korean"){

        changeItem = item_1;

    }

    else if(selectItem == "English"){

        changeItem = item_2;

    }

    $('#sel_module').empty();

    for(var count = 1; count < changeItem.length; count++) {                

        var option = $("<option value='"+changeItem[count]+"'>"+changeItem[count]+"</option>");

        $('#sel_module').append(option);

    }

}

<select name="language" id="sel_language" onchange="language_change();">

    <option value="" selected>언어선택</option>

    <option value="Korean" >Korean</option>

    <option value="English" >English</option>

</select>

<select name="module" id="sel_module">

    <option value="" selected>모듈선택</option>

</select>