snapshot: preserve admin i18n and language stability hardening

backend/workflows/forms.py

@@ -326,6 +326,8 @@ class OnboardingRequestForm(forms.ModelForm):
 
     def save(self, commit=True):
         instance = super().save(commit=False)
+        if not (instance.preferred_language or '').strip():
+            instance.preferred_language = (get_language() or 'de').split('-')[0]
 
         instance.group_mailboxes_required = self.cleaned_data.get('group_mailboxes_required_choice') == 'ja'
         instance.additional_software_needed = self.cleaned_data.get('additional_software_needed_choice') == 'ja'