fix for django 2.1/2.2

django_postgres_extensions/admin/options.py

@@ -1,9 +1,11 @@
 from django.contrib.admin.options import ModelAdmin
-from django.utils.translation import string_concat, ugettext as _
+from django.utils.translation import ugettext as _
+from django.utils.text import format_lazy
 from django.forms.widgets import CheckboxSelectMultiple, SelectMultiple
 from django_postgres_extensions.models import ArrayManyToManyField
 from django.contrib.admin import widgets
 
+
 class PostgresAdmin(ModelAdmin):
 
     def formfield_for_manytomany(self, db_field, request=None, **kwargs):
@@ -35,7 +37,7 @@ def formfield_for_manytomany(self, db_field, request=None, **kwargs):
         if isinstance(form_field.widget, SelectMultiple) and not isinstance(form_field.widget, CheckboxSelectMultiple):
             msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
             help_text = form_field.help_text
-            form_field.help_text = string_concat(help_text, ' ', msg) if help_text else msg
+            form_field.help_text = format_lazy('{} {}', (help_text, msg)) if help_text else msg
         return form_field
 
     def formfield_for_dbfield(self, db_field, request, **kwargs):
@@ -70,4 +72,4 @@ def formfield_for_dbfield(self, db_field, request, **kwargs):
 
             return formfield
         else:
-            return super(PostgresAdmin, self).formfield_for_dbfield(db_field, request, **kwargs)
+            return super(PostgresAdmin, self).formfield_for_dbfield(db_field, request, **kwargs)