feat(languages): add Serbian 10k (Fooftilly) (#5603)

* Add Serbian 10k option

* Add Serbian to groups and list

* Removed potentially problematic words

* fixed names

Author: Fooftilly

frontend/static/languages/_groups.json

@@ -320,7 +320,7 @@
   },
   {
     "name": "serbian",
-    "languages": ["serbian", "serbian_latin"]
+    "languages": ["serbian", "serbian_latin", "serbian_10k", "serbian_latin_10k"]
   },
   {
     "name": "georgian",

frontend/static/languages/_list.json

@@ -190,7 +190,9 @@
   ,"swedish_1k"
   ,"swedish_diacritics"
   ,"serbian_latin"
+  ,"serbian_latin_10k"
   ,"serbian"
+  ,"serbian_10k"
   ,"yoruba_1k"
   ,"swahili_1k"
   ,"maori_1k"