form instance is binded to the widget to retrieve page instance

client/src/components/ChooserWidget/PageChooserWidget.js

@@ -34,6 +34,7 @@ export class PageChooser extends Chooser {
       matchSubclass: this.opts.matchSubclass,
       canChooseRoot: this.opts.canChooseRoot,
       userPerms: this.opts.userPerms,
+      parentId: this.opts.parentId,
     };
     if (this.state && this.state.parentId) {
       opts.parentId = this.state.parentId;

wagtail/admin/forms/pages.py

@@ -1,5 +1,6 @@
 from django import forms
 from django.conf import settings
+from django.forms import models
 from django.utils.translation import gettext as _
 from django.utils.translation import ngettext
 
@@ -153,6 +154,15 @@ class WagtailAdminPageForm(WagtailAdminModelForm):
 
         self.parent_page = parent_page
 
+        # bind the parent page of this forms page to the PageChooser widget
+        for obj in self.fields.values():
+            if isinstance(obj, models.ModelChoiceField):
+                try:
+                    obj.widget.form_instance = self
+                except AttributeError:
+                    # Then propably it isn't a page chooser
+                    pass
+
         if not self.show_comments_toggle:
             del self.fields["comment_notifications"]
 

wagtail/admin/views/chooser.py

@@ -295,6 +295,9 @@ class BrowseView(View):
                     active_locale_id = selected_locale.pk
                 else:
                     active_locale_id = Locale.get_active().pk
+                    selected_locale = get_object_or_404(
+                        Locale, language_code=active_locale_id
+                    )
 
                 # we are at the Root level, so get the locales from the current pages
                 choose_url = reverse("wagtailadmin_choose_page")

wagtail/admin/widgets/chooser.py

@@ -224,6 +224,7 @@ class AdminPageChooser(BaseChooser):
     icon = "doc-empty-inverse"
     classname = "page-chooser"
     js_constructor = "PageChooser"
+    form_instance = None
 
     def __init__(
         self, target_models=None, can_choose_root=False, user_perms=None, **kwargs
@@ -298,9 +299,15 @@ class AdminPageChooser(BaseChooser):
     def get_js_init_options(self, id_, name, value_data):
         opts = super().get_js_init_options(id_, name, value_data)
         value_data = value_data or {}
+
+        # the parentId is set to the current instances id, if the current page instance
+        # exists i.e. EditView, else set to the parent page id since the current
+        # instance doesn't exist yet. i.e CreateView
+        page_id = self.form_instance.instance.id or self.form_instance.parent_page.id
+
         parent_id = value_data.get("parent_id")
         if parent_id is not None:
-            opts["parentId"] = parent_id
+            opts["parentId"] = parent_id or page_id
         return opts
 
     @property