Use monkey patching to override proposal title size

app/forms/concerns/decidim/proposals/admin/proposal_form_override.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module Decidim
+  module Proposals
+    module Admin
+      module ProposalFormOverride
+        extend ActiveSupport::Concern
+
+        included do
+          translatable_attribute :title, String do |field, _locale|
+            validates field, length: { in: 15..250 }, if: proc { |resource| resource.send(field).present? }
+          end
+        end
+      end
+    end
+  end
+end

app/forms/concerns/decidim/proposals/proposal_wizard_create_step_form_override.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Decidim
+  module Proposals
+    module ProposalWizardCreateStepFormOverride
+      extend ActiveSupport::Concern
+
+      included do
+        validates :title, length: { in: 15..250 }
+      end
+    end
+  end
+end

config/initializers/decidim_overrides.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  Decidim::Proposals::ProposalWizardCreateStepForm.include(Decidim::Proposals::ProposalWizardCreateStepFormOverride)
+  Decidim::Proposals::Admin::ProposalForm.include(Decidim::Proposals::Admin::ProposalFormOverride)
+end

spec/lib/overrides_spec.rb

@@ -6,6 +6,13 @@
 # as the expected. If this test fails, it means that the overriden
 # file should be updated to match any change/bug fix introduced in the core
 checksums = [
+  {
+    package: "decidim-proposals",
+    files: {
+      "/app/forms/decidim/proposals/proposal_wizard_create_step_form.rb" => "b495d37088ecebcbe4ac9563bb3498d5",
+      "/app/forms/decidim/proposals/admin/proposal_form.rb" => "fc671fc489c75bb3c190b1da09689c67"
+    }
+  },
   {
     package: "decidim-direct_verifications",
     files: {