diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 5f54f4bdee7..78ae5c5d697 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -33,6 +33,7 @@ class ApplicationController < ActionController::Base
   prepend_before_action :set_locale
   before_action :disable_caching
   before_action :cache_issuer_in_cookie
+  after_action :store_web_locale_in_session
 
   def session_expires_at
     return if @skip_session_expiration || @skip_session_load
@@ -400,6 +401,12 @@ def set_locale
     I18n.locale = LocaleChooser.new(params[:locale], request).locale
   end
 
+  def store_web_locale_in_session
+    return unless user_signed_in?
+
+    user_session[:web_locale] = I18n.locale.to_s
+  end
+
   def pii_requested_but_locked?
     if resolved_authn_context_result.identity_proofing? || resolved_authn_context_result.ialmax?
       current_user.identity_verified? &&
diff --git a/app/presenters/openid_connect_user_info_presenter.rb b/app/presenters/openid_connect_user_info_presenter.rb
index b918b74a681..e7aad1f3cfd 100644
--- a/app/presenters/openid_connect_user_info_presenter.rb
+++ b/app/presenters/openid_connect_user_info_presenter.rb
@@ -20,6 +20,7 @@ def user_info
     }
 
     info[:all_emails] = all_emails_from_sp_identity(identity) if scoper.all_emails_requested?
+    info[:locale] = web_locale if scoper.locale_requested?
     info.merge!(ial2_attributes) if identity_proofing_requested_for_verified_user?
     info.merge!(x509_attributes) if scoper.x509_scopes_requested?
     info[:verified_at] = verified_at if scoper.verified_at_requested?
@@ -57,6 +58,10 @@ def all_emails_from_sp_identity(identity)
     identity.user.confirmed_email_addresses.map(&:email)
   end
 
+  def web_locale
+    out_of_band_session_accessor.load_web_locale
+  end
+
   def ial2_attributes
     {
       given_name: stringify_attr(ial2_data.first_name),
diff --git a/app/presenters/saml_requested_attributes_presenter.rb b/app/presenters/saml_requested_attributes_presenter.rb
index 80ee77dfa5b..763854969a4 100644
--- a/app/presenters/saml_requested_attributes_presenter.rb
+++ b/app/presenters/saml_requested_attributes_presenter.rb
@@ -4,6 +4,7 @@ class SamlRequestedAttributesPresenter
   ATTRIBUTE_TO_FRIENDLY_NAME_MAP = {
     email: :email,
     all_emails: :all_emails,
+    locale: :locale,
     first_name: :given_name,
     last_name: :family_name,
     dob: :birthdate,
@@ -30,6 +31,7 @@ def requested_attributes
     else
       attrs = [:email]
       attrs << :all_emails if bundle.include?(:all_emails)
+      attrs << :locale if bundle.include?(:locale)
       attrs << :verified_at if bundle.include?(:verified_at)
       attrs
     end
diff --git a/app/services/attribute_asserter.rb b/app/services/attribute_asserter.rb
index bba5ac0689e..32eb6222cd4 100644
--- a/app/services/attribute_asserter.rb
+++ b/app/services/attribute_asserter.rb
@@ -36,6 +36,7 @@ def build
     attrs = default_attrs
     add_email(attrs) if bundle.include? :email
     add_all_emails(attrs) if bundle.include? :all_emails
+    add_locale(attrs) if bundle.include? :locale
     add_bundle(attrs) if should_add_proofed_attributes?
     add_verified_at(attrs) if bundle.include?(:verified_at) && ial2_service_provider?
     if authn_request.requested_vtr_authn_contexts.present?
@@ -208,6 +209,10 @@ def add_email(attrs)
     }
   end
 
+  def add_locale(attrs)
+    attrs[:locale] = { getter: ->(_principal) { user_session[:web_locale] } }
+  end
+
   def add_all_emails(attrs)
     attrs[:all_emails] = {
       getter: ->(principal) { principal.confirmed_email_addresses.map(&:email) },
diff --git a/app/services/openid_connect_attribute_scoper.rb b/app/services/openid_connect_attribute_scoper.rb
index 0886ab7230c..814180ca9cb 100644
--- a/app/services/openid_connect_attribute_scoper.rb
+++ b/app/services/openid_connect_attribute_scoper.rb
@@ -20,6 +20,7 @@ class OpenidConnectAttributeScoper
   VALID_SCOPES = (%w[
     email
     all_emails
+    locale
     openid
     profile:verified_at
   ] + X509_SCOPES + IAL2_SCOPES).freeze
@@ -27,6 +28,7 @@ class OpenidConnectAttributeScoper
   VALID_IAL1_SCOPES = (%w[
     email
     all_emails
+    locale
     openid
     profile:verified_at
   ] + X509_SCOPES).freeze
@@ -35,6 +37,7 @@ class OpenidConnectAttributeScoper
     email: %w[email],
     email_verified: %w[email],
     all_emails: %w[all_emails],
+    locale: %w[locale],
     address: %w[address],
     phone: %w[phone],
     phone_verified: %w[phone],
@@ -82,6 +85,10 @@ def all_emails_requested?
     scopes.include?('all_emails')
   end
 
+  def locale_requested?
+    scopes.include?('locale')
+  end
+
   def filter(user_info)
     user_info.select do |key, _v|
       !ATTRIBUTE_SCOPES_MAP.key?(key) || (scopes & ATTRIBUTE_SCOPES_MAP[key]).present?
diff --git a/app/services/out_of_band_session_accessor.rb b/app/services/out_of_band_session_accessor.rb
index da497b440dd..cad4749a67c 100644
--- a/app/services/out_of_band_session_accessor.rb
+++ b/app/services/out_of_band_session_accessor.rb
@@ -39,6 +39,11 @@ def load_pii(profile_id)
     Pii::Cacher.new(nil, session).fetch(profile_id) if session
   end
 
+  # @return [String, nil]
+  def load_web_locale
+    session_data.dig('warden.user.user.session', :web_locale)
+  end
+
   # @return [X509::Attributes]
   def load_x509
     X509::Attributes.new_from_json(session_data.dig('warden.user.user.session', :decrypted_x509))
@@ -83,6 +88,13 @@ def put_x509(piv_cert_info, expiration = 5.minutes)
     put(data, expiration)
   end
 
+  # @api private
+  # Only used for convenience in tests
+  # @param [String] locale
+  def put_locale(locale, expiration = 5.minutes)
+    put({ web_locale: locale }, expiration)
+  end
+
   # @api private
   # Only used for convenience in tests
   def exists?
@@ -92,15 +104,16 @@ def exists?
   private
 
   def put(data, expiration = 5.minutes)
-    session_data = {
-      'warden.user.user.session' => data.to_h,
+    existing_user_session = session_data.dig('warden.user.user.session')
+    new_session_data = {
+      'warden.user.user.session' => data.to_h.merge(existing_user_session.to_h),
     }
 
     session_store.send(
       :write_session,
       PLACEHOLDER_REQUEST,
       Rack::Session::SessionId.new(session_uuid),
-      session_data,
+      new_session_data,
       expire_after: expiration.to_i,
     )
   end
diff --git a/spec/controllers/sign_up/passwords_controller_spec.rb b/spec/controllers/sign_up/passwords_controller_spec.rb
index e0979324944..6b6769b0bf2 100644
--- a/spec/controllers/sign_up/passwords_controller_spec.rb
+++ b/spec/controllers/sign_up/passwords_controller_spec.rb
@@ -94,6 +94,7 @@
           'last_request_at' => kind_of(Numeric),
           new_device: false,
           in_account_creation_flow: true,
+          web_locale: 'en',
         )
       end
     end
diff --git a/spec/features/openid_connect/openid_connect_spec.rb b/spec/features/openid_connect/openid_connect_spec.rb
index 7a113b24b0f..f743a6227a8 100644
--- a/spec/features/openid_connect/openid_connect_spec.rb
+++ b/spec/features/openid_connect/openid_connect_spec.rb
@@ -569,6 +569,39 @@
     expect(userinfo_response[:verified_at]).to be_nil
   end
 
+  it 'returns the locale if requested', driver: :mobile_rack_test do
+    user = user_with_2fa
+
+    token_response = sign_in_get_token_response(
+      user: user,
+      scope: 'openid email locale',
+      sign_in_steps: proc do
+        visit root_path(locale: 'es')
+
+        fill_in_credentials_and_submit(
+          user.confirmed_email_addresses.first.email,
+          user.password,
+        )
+        fill_in_code_with_last_phone_otp
+        click_submit_default
+      end,
+      handoff_page_steps: proc do
+        click_agree_and_continue
+      end,
+    )
+
+    access_token = token_response[:access_token]
+    expect(access_token).to be_present
+
+    page.driver.get api_openid_connect_userinfo_path,
+                    {},
+                    'HTTP_AUTHORIZATION' => "Bearer #{access_token}"
+
+    userinfo_response = JSON.parse(page.body).with_indifferent_access
+    expect(userinfo_response[:email]).to eq(user.email)
+    expect(userinfo_response[:locale]).to eq('es')
+  end
+
   it 'errors if verified_within param is too recent', driver: :mobile_rack_test do
     client_id = 'urn:gov:gsa:openidconnect:test'
     allow(IdentityConfig.store).to receive(:allowed_verified_within_providers)
@@ -1087,6 +1120,7 @@ def sign_in_get_token_response(
     acr_values: Saml::Idp::Constants::IAL1_AUTHN_CONTEXT_CLASSREF,
     scope: 'openid email',
     redirect_uri: 'gov.gsa.openidconnect.test://result',
+    sign_in_steps: nil,
     handoff_page_steps: nil,
     proofing_steps: nil,
     verified_within: nil,
@@ -1114,7 +1148,11 @@ def sign_in_get_token_response(
       verified_within: verified_within,
     )
 
-    _user = sign_in_live_with_2fa(user)
+    if sign_in_steps.present?
+      sign_in_steps.call
+    else
+      sign_in_live_with_2fa(user)
+    end
 
     proofing_steps&.call
     handoff_page_steps&.call
diff --git a/spec/features/saml/ial1_sso_spec.rb b/spec/features/saml/ial1_sso_spec.rb
index bc73dbf0abe..5fd8a166e48 100644
--- a/spec/features/saml/ial1_sso_spec.rb
+++ b/spec/features/saml/ial1_sso_spec.rb
@@ -238,4 +238,35 @@
       expect(xmldoc.attribute_value_for('verified_at')).to be_blank
     end
   end
+
+  context 'requesting locale' do
+    it 'includes locale in the response' do
+      user = create(:user, :fully_registered)
+      saml_authn_request = saml_authn_request_url(
+        overrides: {
+          issuer: sp1_issuer,
+          authn_context: [
+            Saml::Idp::Constants::IAL1_AUTHN_CONTEXT_CLASSREF,
+            "#{Saml::Idp::Constants::REQUESTED_ATTRIBUTES_CLASSREF}email,locale",
+          ],
+        },
+      )
+
+      visit saml_authn_request
+      visit root_url(locale: 'es')
+      fill_in_credentials_and_submit(user.email, user.password)
+      fill_in_code_with_last_phone_otp
+      click_submit_default
+
+      expect(current_url).to match new_user_session_path
+      click_submit_default
+      click_agree_and_continue
+      click_submit_default
+
+      xmldoc = SamlResponseDoc.new('feature', 'response_assertion')
+
+      expect(xmldoc.attribute_node_for('locale')).to be_present
+      expect(xmldoc.attribute_value_for('locale')).to eq('es')
+    end
+  end
 end
diff --git a/spec/presenters/openid_connect_user_info_presenter_spec.rb b/spec/presenters/openid_connect_user_info_presenter_spec.rb
index 2af4dc32ab0..2237272d621 100644
--- a/spec/presenters/openid_connect_user_info_presenter_spec.rb
+++ b/spec/presenters/openid_connect_user_info_presenter_spec.rb
@@ -5,7 +5,7 @@
 
   let(:rails_session_id) { SecureRandom.uuid }
   let(:scope) do
-    'openid email all_emails address phone profile social_security_number x509'
+    'openid email all_emails locale address phone profile social_security_number x509'
   end
   let(:service_provider_ial) { 2 }
   let(:service_provider) { create(:service_provider, ial: service_provider_ial) }
@@ -13,6 +13,7 @@
   let(:vtr) { ['C1.C2.P1'] }
   let(:acr_values) { nil }
   let(:requested_aal_value) { nil }
+  let(:locale) { 'en' }
   let(:identity) do
     build(
       :service_provider_identity,
@@ -26,6 +27,10 @@
     )
   end
 
+  before do
+    OutOfBandSessionAccessor.new(rails_session_id).put_locale(locale, 5.minutes.in_seconds)
+  end
+
   subject(:presenter) { OpenidConnectUserInfoPresenter.new(identity) }
 
   describe '#user_info' do
@@ -61,7 +66,7 @@
 
       context 'no identity proofing' do
         let(:vtr) { ['C1.C2'] }
-        let(:scope) { 'openid email all_emails' }
+        let(:scope) { 'openid email all_emails locale' }
 
         it 'includes the correct attributes' do
           aggregate_failures do
@@ -70,6 +75,7 @@
             expect(user_info[:email]).to eq(identity.user.email_addresses.first.email)
             expect(user_info[:email_verified]).to eq(true)
             expect(user_info[:all_emails]).to eq([identity.user.email_addresses.first.email])
+            expect(user_info[:locale]).to eq(locale)
             expect(user_info).to_not have_key(:ial)
             expect(user_info).to_not have_key(:aal)
             expect(user_info[:vot]).to eq('C1.C2')
@@ -79,7 +85,9 @@
 
       context 'identity proofing' do
         let(:vtr) { ['C1.C2.P1'] }
-        let(:scope) { 'openid email all_emails address phone profile social_security_number' }
+        let(:scope) do
+          'openid email all_emails locale address phone profile social_security_number'
+        end
 
         it 'includes the correct non-proofed attributes' do
           aggregate_failures do
@@ -88,6 +96,7 @@
             expect(user_info[:email]).to eq(identity.user.email_addresses.first.email)
             expect(user_info[:email_verified]).to eq(true)
             expect(user_info[:all_emails]).to eq([identity.user.email_addresses.first.email])
+            expect(user_info[:locale]).to eq(locale)
             expect(user_info).to_not have_key(:ial)
             expect(user_info).to_not have_key(:aal)
             expect(user_info[:vot]).to eq('C1.C2.P1')
@@ -126,7 +135,7 @@
           ].join(' ')
         end
         let(:requested_aal_value) { Saml::Idp::Constants::AAL2_AUTHN_CONTEXT_CLASSREF }
-        let(:scope) { 'openid email all_emails' }
+        let(:scope) { 'openid email all_emails locale' }
 
         it 'includes the correct attributes' do
           aggregate_failures do
@@ -135,6 +144,7 @@
             expect(user_info[:email]).to eq(identity.user.email_addresses.first.email)
             expect(user_info[:email_verified]).to eq(true)
             expect(user_info[:all_emails]).to eq([identity.user.email_addresses.first.email])
+            expect(user_info[:locale]).to eq(locale)
             expect(user_info[:ial]).to eq(Saml::Idp::Constants::IAL1_AUTHN_CONTEXT_CLASSREF)
             expect(user_info[:aal]).to eq(Saml::Idp::Constants::AAL2_AUTHN_CONTEXT_CLASSREF)
             expect(user_info).to_not have_key(:vot)
@@ -150,7 +160,9 @@
           ].join(' ')
         end
         let(:requested_aal_value) { Saml::Idp::Constants::AAL2_AUTHN_CONTEXT_CLASSREF }
-        let(:scope) { 'openid email all_emails address phone profile social_security_number' }
+        let(:scope) do
+          'openid email all_emails locale address phone profile social_security_number'
+        end
 
         it 'includes the correct non-proofed attributes' do
           aggregate_failures do
@@ -159,6 +171,7 @@
             expect(user_info[:email]).to eq(identity.user.email_addresses.first.email)
             expect(user_info[:email_verified]).to eq(true)
             expect(user_info[:all_emails]).to eq([identity.user.email_addresses.first.email])
+            expect(user_info[:locale]).to eq(locale)
             expect(user_info[:ial]).to eq(Saml::Idp::Constants::IAL2_AUTHN_CONTEXT_CLASSREF)
             expect(user_info[:aal]).to eq(Saml::Idp::Constants::AAL2_AUTHN_CONTEXT_CLASSREF)
             expect(user_info).to_not have_key(:vot)
@@ -199,6 +212,7 @@
               expect(user_info[:email]).to eq(identity.user.email_addresses.first.email)
               expect(user_info[:email_verified]).to eq(true)
               expect(user_info[:all_emails]).to eq([identity.user.email_addresses.first.email])
+              expect(user_info[:locale]).to eq(locale)
               expect(user_info[:ial]).to eq(
                 Saml::Idp::Constants::IAL2_BIO_REQUIRED_AUTHN_CONTEXT_CLASSREF,
               )
@@ -236,7 +250,9 @@
           ].join(' ')
         end
         let(:requested_aal_value) { Saml::Idp::Constants::AAL2_AUTHN_CONTEXT_CLASSREF }
-        let(:scope) { 'openid email all_emails address phone profile social_security_number' }
+        let(:scope) do
+          'openid email all_emails locale address phone profile social_security_number'
+        end
 
         context 'the user has verified their identity' do
           it 'includes the proofed attributes' do
@@ -286,7 +302,7 @@
 
     context 'when minimal scopes are requested for proofed attributes' do
       let(:scope) do
-        'openid email all_emails profile'
+        'openid email all_emails locale profile'
       end
 
       it 'only returns the requested attributes' do
diff --git a/spec/services/attribute_asserter_spec.rb b/spec/services/attribute_asserter_spec.rb
index 59055c719aa..d240451da3d 100644
--- a/spec/services/attribute_asserter_spec.rb
+++ b/spec/services/attribute_asserter_spec.rb
@@ -7,7 +7,7 @@
   let(:facial_match_verified_user) do
     create(:profile, :active, :verified, idv_level: :in_person).user
   end
-  let(:user_session) { {} }
+  let(:user_session) { { web_locale: 'en' } }
   let(:identity) do
     build(
       :service_provider_identity,
@@ -615,6 +615,19 @@
         end
       end
 
+      context 'custom bundle includes locale' do
+        let(:attribute_bundle) { %w[locale] }
+        before do
+          subject.build
+        end
+
+        it 'includes the user locale' do
+          locale_getter = user.asserted_attributes[:locale][:getter]
+          locale = locale_getter.call(user)
+          expect(locale).to eq('en')
+        end
+      end
+
       context 'custom bundle includes email, phone' do
         let(:attribute_bundle) { %w[first_name last_name email phone] }
         before do
diff --git a/spec/services/openid_connect_attribute_scoper_spec.rb b/spec/services/openid_connect_attribute_scoper_spec.rb
index facbf222fee..957d443e0cf 100644
--- a/spec/services/openid_connect_attribute_scoper_spec.rb
+++ b/spec/services/openid_connect_attribute_scoper_spec.rb
@@ -35,6 +35,7 @@
         email: 'foo@example.com',
         email_verified: true,
         all_emails: ['foo@example.com', 'bar@example.com'],
+        locale: 'es',
         given_name: 'John',
         family_name: 'Jones',
         birthdate: '1970-01-01',
@@ -89,6 +90,14 @@
       end
     end
 
+    context 'with the locale scope' do
+      let(:scope) { 'openid locale' }
+
+      it 'includes the locale attribute' do
+        expect(filtered[:locale]).to eq('es')
+      end
+    end
+
     context 'with phone scope' do
       let(:scope) { 'openid phone' }
 
diff --git a/spec/services/out_of_band_session_accessor_spec.rb b/spec/services/out_of_band_session_accessor_spec.rb
index 68f414ab2be..0a3fb23d5c7 100644
--- a/spec/services/out_of_band_session_accessor_spec.rb
+++ b/spec/services/out_of_band_session_accessor_spec.rb
@@ -4,6 +4,11 @@
   let(:session_uuid) { SecureRandom.uuid }
   let(:profile_id) { 123 }
 
+  # This test uses a separate writer instance to write test data to the session store.
+  # The OutOfBandSessionAccessor memoizes the data that it reads from the session.
+  # Writes require reads to merge test data properly for subsequent writes.
+  subject(:writer_instance) { described_class.new(session_uuid) }
+
   subject(:store) { described_class.new(session_uuid) }
 
   around do |ex|
@@ -24,9 +29,18 @@
     end
   end
 
+  describe '#load_web_locale' do
+    it 'loads the web_locale from the session' do
+      writer_instance.put_locale('es')
+
+      web_locale = store.load_web_locale
+      expect(web_locale).to eq('es')
+    end
+  end
+
   describe '#load_pii' do
     it 'loads PII from the session' do
-      store.put_pii(
+      writer_instance.put_pii(
         profile_id: profile_id,
         pii: { dob: '1970-01-01' },
         expiration: 5.minutes.in_seconds,
@@ -40,7 +54,7 @@
 
   describe '#load_x509' do
     it 'loads X509 attributes from the session' do
-      store.put_x509({ subject: 'O=US, OU=DoD, CN=John.Doe.1234' }, 5.minutes.in_seconds)
+      writer_instance.put_x509({ subject: 'O=US, OU=DoD, CN=John.Doe.1234' }, 5.minutes.in_seconds)
 
       x509 = store.load_x509
       expect(x509).to be_kind_of(X509::Attributes)
@@ -50,7 +64,7 @@
 
   describe '#destroy' do
     it 'destroys the session' do
-      store.put_pii(
+      writer_instance.put_pii(
         profile_id: profile_id,
         pii: { first_name: 'Fakey' },
         expiration: 5.minutes.in_seconds,