In terms of the re-conferral of Vietnamese citizenship, under the current Law on Vietnamese Citizenship, each Vietnamese citizen has a single Vietnamese nationality, so an overseas Vietnamese having foreign citizenships who wishes to re-acquire Vietnamese nationality is required to stop his/her current foreign citizenships; and this will be settled under the laws of the countries in which he/she lives, and the Vietnamese State is not in a position to intervene in these cases.
For further information: Overseas Vietnamese can access to http://mienthithucvk.mofa.gov.vn newly launched by the Ministry of Foreign Affairs to obtain stipulations on visa exemption.
http://www.gov.vn