>>>viet= "â ă á à ấ ầ ắ ằ ạ ậ  ặ "

>>>print(viet)


Traceback (most recent call last):
  File "tiengviet.py", line 4, in <module>
    print(viet)
  File "I:\python\python.v3.1_portable\App\lib\encodings\cp1252.py",
line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode character '\u0103' in
position 2: character maps to <undefined>
>Exit code: 1

how to fix it ?

Change your terminal's encoding.

It looks like you are using the Windows terminal, that, afaik, is not
able to display the characters you are trying to print. This is because
its default encoding - cp1252 - can encode only a small subset of the
Unicode characters.
If changing the encoding of the terminal doesn't work, you can try to
use a better terminal or IDLE instead.