If theme change fails, also log error message on the server and pass …

…the ValidationError message to frontend

pontoon/contributors/views.py

@@ -1,4 +1,5 @@
 import json
+import logging
 
 from dateutil.relativedelta import relativedelta
 from django.contrib import messages
@@ -26,6 +27,9 @@
 from pontoon.uxactionlog.utils import log_ux_action
 
 
+log = logging.getLogger(__name__)
+
+
 @login_required(redirect_field_name="", login_url="/403")
 def profile(request):
     """Current user profile."""
@@ -210,9 +214,11 @@ def toggle_theme(request, username):
         profile.theme = theme
         profile.full_clean()
         profile.save()
-    except ValidationError:
+    except ValidationError as e:
+        error_message = f"User profile validation error: {e}"
+        log.error(error_message)
         return JsonResponse(
-            {"status": False, "message": "Bad Request: Invalid theme"},
+            {"status": False, "message": error_message},
             status=400,
         )