Update `Bengali` translation

Currently translated at 87.7% (172 of 196 strings)

Translation: Wiki-Bot/Dashboard
Translate-URL: https://translate.wikibot.de/projects/wiki-bot/dashboard/bn/

dashboard/i18n/bn.json

@@ -1,6 +1,6 @@
 {
     "fallback": [
-        " ",
+        "en",
         " ",
         " ",
         " ",