Update `Bengali` translation

Currently translated at 5.7% (7 of 122 strings)

Translation: Wiki-Bot/Dashboard
Translate-URL: https://weblate.frisk.space/projects/wiki-bot/dashboard/bn/

dashboard/i18n/bn.json

@@ -1,4 +1,11 @@
 {
+    "fallback": [
+        " ",
+        " ",
+        " ",
+        "en",
+        " "
+    ],
     "general": {
         "settings": "সেটিংস",
         "title": "উইকি-বট সেটিংস"