Translate to Vietnamese

[sontl]

Description

Add languagle translation for Vietnamese

Closes #(issue_number)

Checklist:

• [x] I have read the Contribution Guidelines
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings

Contributor License Agreement

By submitting this pull request, I acknowledge and agree that my contributions will be included in Stirling-PDF and that they can be relicensed in the future under the MPL 2.0 (Mozilla Public License Version 2.0) license.

(This does not change the general open-source nature of Stirling-PDF, simply moving from one license to another license)