the .mst files that you found in 1C:Enterprise distribution kit are not related to interface languages. You have to create a new transformation.
1. Open the .msi file in Orca.
2. On the Transform menu, click New Transform.
3. In the Property table, set DEFLANGUAGE to vi.
4. On the Transform menu, click Generate Transform and save the .mst file.
5. On the Transform menu, click Close Transform.
This gives you both English and Vietnamese because the English interface cannot be removed from the platform.