Add password protection feature in MultiChatDialog: Implement room password management, including prompts for password entry and error handling for invalid passwords. Update i18n files with localized messages for password prompts in English, German, and Spanish.

frontend/src/i18n/locales/en/chat.json

@@ -114,6 +114,12 @@
                     "servicesStatus": "Service status"
                 },
                 "types": {}
+            },
+            "password": {
+                "requiredPrompt": "Room \"{room}\" is password-protected. Please enter password:",
+                "invalidPrompt": "Wrong password for \"{room}\". Please try again:",
+                "cancelled": "Join to \"{room}\" was cancelled.",
+                "empty": "Password must not be empty."
             }
         },
         "randomchat": {