feat: Translate frontend/src/i18n/en.json in bg

54% of minimum 50% translated source file: 'frontend/src/i18n/en.json'
on 'bg'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

frontend/src/i18n/bg.json

@@ -145,7 +145,7 @@
     "uploadMessage": "Изберете опция за качване.",
     "optionalPassword": "Опционална парола",
     "resolution": "Резолюция",
-    "discardEditorChanges": "Are you sure you wish to discard the changes you've made?"
+    "discardEditorChanges": "Сигурни ли сте, че искате да откажете направените промени?"
   },
   "search": {
     "images": "Images",