Translate to Vietnamese (#1591)

* Translate to Vietnamese

* Add translation for Vietnamese

* - Remove  invalid properties and duplicated values.
- Add blank lines to align with the original format of en_GB file

* fix eof

* add empty lines to align with the template format. The number of line is equal with the reference en_GB file now

* change some translations to be more natural and easier to understand

src/main/resources/templates/fragments/languages.html

@@ -32,4 +32,5 @@
                       <a class="dropdown-item lang_dropdown-item" href="" data-bs-language-code="hr_HR"> <img th:src="@{'/images/flags/hr.svg'}" alt="icon" width="20" height="15"> Hrvatski</a>
                       <a class="dropdown-item lang_dropdown-item" href="" data-bs-language-code="no_NB"> <img th:src="@{'/images/flags/no.svg'}" alt="icon" width="20" height="15"> Norsk</a>
                       <a class="dropdown-item lang_dropdown-item" href="" data-bs-language-code="th_TH"> <img th:src="@{'/images/flags/th.svg'}" alt="icon" width="20" height="15"> ไทย</a>
+                      <a class="dropdown-item lang_dropdown-item" href="" data-bs-language-code="vi_VN"> <img th:src="@{'/images/flags/vn.svg'}" alt="icon" width="20" height="15"> Tiếng Việt</a>
 </th:block>