Vietnamese characters are garbled after export and import

问题

I exported a table in Oracle (which has Vietnamese text) from computer A with::

exp system/***** BUFFER=64000 FILE=/tmp/export.dmp TABLES=(USERS.AREA) GRANTS=N INDEXES=NO ROWS=Y

Then I imported that dump file on computer B (Centos same as A)

imp system/***** file="/tmp/export_table.dmp" 

But when I query in SQL*Plus I see question marks instead of Vietnamese characters:

SELECT AREA_ID,AREA_NAME,COMMENTS FROM USERS.AREA WHERE ROWNUM<2;

I tried setting NLS_LANG="American_Amarica.VN8VN3" on computer A before I execute EXP and IMP command ,but the result was the same.

Then I connected to computer A using a Windows client, Navicat for Oracle. But to my surprise, in one database ,I imported two tables, one is garbled, the other is not.

Questions:

1. Did I export *.dmp incorrectly?
2. Is the computer B environment wrong?
3. Is there an incorrect setting in my Windows Navicat client?
4. How can I solve this problem?

来源：https://stackoverflow.com/questions/39162049/vietnamese-characters-are-garbled-after-export-and-import