You can identify the character code.

Regarding discrimination from the text area
Most browsers send the character code in the currently displayed encoding, so if you enter characters from the initial state and make a judgment, it will be sent in utf-8, which is the character code of the input form.

Example of changing the encoding sent by the browser
Environment: WindowsXP SP3 Internet Explorer 8 * Behavior differs depending on the environment
Select Korean by "Right click" → "Encode"
나는 행정구역을 통폐합하면서 간촌의 '간'자와 석촌 มาล่มสลายเมื่อถูกฝ่ายค้านเปิดอภิปรายไม่ไว้วางใจ
* If you enter Hangul characters for red and Thai for blue , you can see that the characters were sent with CP949 Korean character code.
Also, you can see that Thai words that cannot be mapped by CP949 are sent by numerical character reference (decimal number).
From this, it can be seen that Win / IE8 prioritizes the selected encoding over the character code on which the page is written.