Go to the Bentley Subscription Services Portal and add the Download Role to your Roles and Permissions. Either you or your local account administrator should be able to make this change. Then use the Software Downloads page to locate and download the Vietnamese version of MicroStation that you are interested in.
Subscription Services - https://subscriptionservices.bentley.com/
But I just checked and see that there is not a Vietnamese version listed for download, so please post your Question on the MicroStation Forum for a follow-up.
microstation v8 software
Can I have the Vietnamese version of microstation v8 file?