Set up language fallback for docs, and update translation guidelines (#7403)

* Set up language fallback for docs, and update translation guidelines

* Title Case

* Add ID example

* Link to emoji flag cheatsheet

* Move docs preview section to contributing.md

* Point to docs preview in the readme

docs/index.html

@@ -35,6 +35,15 @@
       loadNavbar: '_langs.md',
       mergeNavbar: true,
       auto2top: true,
+      fallbackLanguages: [
+        'de',
+        'es',
+        'fr-fr',
+        'he-il',
+        'ja',
+        'ru-ru',
+        'zh-cn'
+      ],
       formatUpdated: '{YYYY}/{MM}/{DD} {HH}:{mm}',
       search: {
         paths: 'auto',