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/static/images/flags/vn.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" id="flag-icons-vn" viewBox="0 0 640 480">
+  <defs>
+    <clipPath id="vn-a">
+      <path fill-opacity=".7" d="M-85.3 0h682.6v512H-85.3z"/>
+    </clipPath>
+  </defs>
+  <g fill-rule="evenodd" clip-path="url(#vn-a)" transform="translate(80)scale(.9375)">
+    <path fill="#da251d" d="M-128 0h768v512h-768z"/>
+    <path fill="#ff0" d="M349.6 381 260 314.3l-89 67.3L204 272l-89-67.7 110.1-1 34.2-109.4L294 203l110.1.1-88.5 68.4 33.9 109.6z"/>
+  </g>
+</svg>