diff --git a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexPaymentSessionConverter.kt b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexPaymentSessionConverter.kt
index e973ec0..14d0703 100644
--- a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexPaymentSessionConverter.kt
+++ b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexPaymentSessionConverter.kt
@@ -33,6 +33,7 @@ object AirwallexPaymentSessionConverter {
 
     val currency = sessionMap.getStringOrNull("currency") ?: error("Currency is required")
     val countryCode = sessionMap.getStringOrNull("countryCode") ?: error("Country code is required")
+    val locale = sessionMap.toLocale()
     val paymentIntentId =
       sessionMap.getStringOrNull("paymentIntentId") ?: error("PaymentIntentId is required")
 
@@ -60,6 +61,7 @@ object AirwallexPaymentSessionConverter {
       .setHidePaymentConsents(hidePaymentConsents)
       .setPaymentMethods(paymentMethods)
       .setShipping(shipping)
+      .setLocale(locale)
       .build()
   }
 
diff --git a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringSessionConverter.kt b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringSessionConverter.kt
index 6f67ed8..472cf0f 100644
--- a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringSessionConverter.kt
+++ b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringSessionConverter.kt
@@ -21,6 +21,7 @@ object AirwallexRecurringSessionConverter {
     val currency = sessionMap.getStringOrNull("currency") ?: error("currency is required")
 
     val countryCode = sessionMap.getStringOrNull("countryCode") ?: error("countryCode is required")
+    val locale = sessionMap.toLocale()
 
     val amount = sessionMap.getDoubleOrDefault("amount", -1.0).let {
       if (it == -1.0) error("amount is required")
@@ -54,6 +55,7 @@ object AirwallexRecurringSessionConverter {
       .setReturnUrl(returnUrl)
       .setRequireEmail(isEmailRequired)
       .setPaymentMethods(paymentMethods)
+      .setLocale(locale)
 
     merchantTriggerReason?.let {
       sessionBuilder.setMerchantTriggerReason(merchantTriggerReason)
diff --git a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringWithIntentSessionConverter.kt b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringWithIntentSessionConverter.kt
index 01b5169..9d7a34c 100644
--- a/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringWithIntentSessionConverter.kt
+++ b/android/src/main/java/com/airwallexpaymentreactnative/util/AirwallexRecurringWithIntentSessionConverter.kt
@@ -24,6 +24,7 @@ object AirwallexRecurringWithIntentSessionConverter {
 
     val countryCode = sessionMap.getStringOrNull("countryCode")
       ?: error("countryCode is required")
+    val locale = sessionMap.toLocale()
 
     val amount = sessionMap.getDoubleOrDefault("amount", -1.0).let {
       if (it == -1.0) error("amount is required")
@@ -70,6 +71,7 @@ object AirwallexRecurringWithIntentSessionConverter {
       .setReturnUrl(returnUrl)
       .setAutoCapture(autoCapture)
       .setShipping(shipping)
+      .setLocale(locale)
 
     merchantTriggerReason?.let {
       sessionBuilder.setMerchantTriggerReason(merchantTriggerReason)
diff --git a/android/src/main/java/com/airwallexpaymentreactnative/util/Converter+Extensions.kt b/android/src/main/java/com/airwallexpaymentreactnative/util/Converter+Extensions.kt
index ab8a567..6775e3e 100644
--- a/android/src/main/java/com/airwallexpaymentreactnative/util/Converter+Extensions.kt
+++ b/android/src/main/java/com/airwallexpaymentreactnative/util/Converter+Extensions.kt
@@ -7,6 +7,7 @@ import com.airwallex.android.core.model.PaymentMethod
 import com.airwallex.android.core.model.Shipping
 import com.facebook.react.bridge.ReadableArray
 import com.facebook.react.bridge.ReadableMap
+import java.util.Locale
 
 fun ReadableMap.getStringOrNull(key: String): String? =
   if (hasKey(key)) getString(key) else null
@@ -26,6 +27,9 @@ fun ReadableMap.getArrayOrNull(key: String): ReadableArray? =
 fun ReadableMap.getMapOrNull(key: String): ReadableMap? =
   if (hasKey(key)) getMap(key) else null
 
+fun ReadableMap.toLocale(): Locale? =
+  getStringOrNull("lang")?.let { Locale.forLanguageTag(it.replace('_', '-')) }
+
 fun ReadableMap.toShipping(): Shipping? {
   val firstName = getStringOrNull("firstName") ?: getStringOrNull("first_name")
   val lastName = getStringOrNull("lastName") ?: getStringOrNull("last_name")
diff --git a/example/src/App.tsx b/example/src/App.tsx
index f65549c..df2f221 100644
--- a/example/src/App.tsx
+++ b/example/src/App.tsx
@@ -32,6 +32,10 @@ import type { PaymentResult } from '../../src/types/PaymentResult';
 import { useEffect, useState } from 'react';
 
 import PaymentConsentCreator from './util/PaymentConsentCreator';
+import {
+  DEFAULT_LANG_OPTION,
+  SUPPORTED_LANG_OPTIONS,
+} from './util/supportedLanguages';
 
 type Environment = 'staging' | 'demo' | 'preview';
 type PaymentMode = 'oneOff' | 'recurring' | 'recurringAndPayment';
@@ -63,6 +67,7 @@ function Main() {
   const { showActionSheetWithOptions } = useActionSheet();
   const [loading, setLoading] = useState(false);
   const [paymentMode, setPaymentMode] = useState<PaymentMode>('oneOff');
+  const [selectedLang, setSelectedLang] = useState(DEFAULT_LANG_OPTION);
   const [environment, setEnvironment] = useState<Environment>(DEFAULT_ENV);
   const [paymentService, setPaymentService] = useState(
     new PaymentService(DEFAULT_ENV, '', '')
@@ -131,29 +136,51 @@ function Main() {
     );
   };
 
+  const showLangSheet = () => {
+    const labels = [...SUPPORTED_LANG_OPTIONS, 'Cancel'];
+    showActionSheetWithOptions(
+      {
+        title: 'Language',
+        options: labels,
+        cancelButtonIndex: labels.length - 1,
+      },
+      (selectedIndex) => {
+        if (selectedIndex == null || selectedIndex === labels.length - 1)
+          return;
+        setSelectedLang(SUPPORTED_LANG_OPTIONS[selectedIndex]!);
+      }
+    );
+  };
+
   const paymentModeLabel =
     PAYMENT_MODE_OPTIONS.find((o) => o.value === paymentMode)?.label ??
     'Payment Mode';
 
   async function fetchSession(requireCustomerId = false) {
     setLoading(true);
+    const lang =
+      selectedLang === DEFAULT_LANG_OPTION ? undefined : selectedLang;
     try {
       let session;
       switch (paymentMode) {
         case 'oneOff':
           session = await SessionCreator.createOneOffSession(
             paymentService,
-            requireCustomerId
+            requireCustomerId,
+            lang
           );
           break;
         case 'recurring':
-          session = await SessionCreator.createRecurringSession(paymentService);
+          session = await SessionCreator.createRecurringSession(
+            paymentService,
+            lang
+          );
           break;
         case 'recurringAndPayment':
-          session =
-            await SessionCreator.createRecurringWithIntentSession(
-              paymentService
-            );
+          session = await SessionCreator.createRecurringWithIntentSession(
+            paymentService,
+            lang
+          );
           break;
         default:
           throw new Error('Unknown payment mode');
@@ -279,9 +306,14 @@ function Main() {
           style={styles.loading}
         />
       )}
-      <TouchableOpacity style={styles.picker} onPress={showPaymentModeSheet}>
-        <Text style={styles.pickerText}>{paymentModeLabel}</Text>
-      </TouchableOpacity>
+      <View style={styles.pickerRow}>
+        <TouchableOpacity style={styles.picker} onPress={showPaymentModeSheet}>
+          <Text style={styles.pickerText}>{paymentModeLabel}</Text>
+        </TouchableOpacity>
+        <TouchableOpacity style={styles.picker} onPress={showLangSheet}>
+          <Text style={styles.pickerText}>lang: {selectedLang}</Text>
+        </TouchableOpacity>
+      </View>
 
       <TouchableOpacity
         style={styles.button}
@@ -395,15 +427,21 @@ const styles = StyleSheet.create({
     left: '50%',
     transform: [{ translateX: -25 }, { translateY: -25 }],
   },
+  pickerRow: {
+    flexDirection: 'row',
+    justifyContent: 'center',
+    alignItems: 'center',
+    width: '80%',
+    marginBottom: 20,
+    gap: 16,
+  },
   picker: {
+    flex: 1,
     paddingVertical: 12,
     paddingHorizontal: 10,
     borderWidth: 1,
     borderColor: 'gray',
     borderRadius: 4,
-    width: '80%',
-    alignSelf: 'center',
-    marginBottom: 20,
     alignItems: 'center',
   },
   pickerText: {
diff --git a/example/src/util/SessionCreator.ts b/example/src/util/SessionCreator.ts
index 10e16f0..3f088bc 100644
--- a/example/src/util/SessionCreator.ts
+++ b/example/src/util/SessionCreator.ts
@@ -21,7 +21,8 @@ import { getCustomerParams, getPaymentParams } from '../api/PaymentParams';
 class SessionCreator {
   static async createOneOffSession(
     paymentService: PaymentService,
-    requireCustomerId: boolean = false
+    requireCustomerId: boolean = false,
+    lang?: string
   ): Promise<PaymentSession> {
     try {
       let customerId = null;
@@ -110,6 +111,7 @@ class SessionCreator {
         autoCapture: true,
         hidePaymentConsents: false,
         clientSecret: clientSecret,
+        lang,
       };
       return session;
     } catch (error) {
@@ -119,7 +121,8 @@ class SessionCreator {
   }
 
   static async createRecurringSession(
-    paymentService: PaymentService
+    paymentService: PaymentService,
+    lang?: string
   ): Promise<PaymentSession> {
     try {
       const customerInfo =
@@ -150,6 +153,7 @@ class SessionCreator {
         returnUrl: '',
         nextTriggeredBy: NextTriggeredBy.Merchant,
         merchantTriggerReason: MerchantTriggerReason.Scheduled,
+        lang,
       };
       return session;
     } catch (error) {
@@ -159,7 +163,8 @@ class SessionCreator {
   }
 
   static async createRecurringWithIntentSession(
-    paymentService: PaymentService
+    paymentService: PaymentService,
+    lang?: string
   ): Promise<PaymentSession> {
     try {
       const customerInfo =
@@ -205,6 +210,7 @@ class SessionCreator {
         returnUrl: '',
         nextTriggeredBy: NextTriggeredBy.Merchant,
         merchantTriggerReason: MerchantTriggerReason.Scheduled,
+        lang,
       };
       return session;
     } catch (error) {
diff --git a/example/src/util/supportedLanguages.ts b/example/src/util/supportedLanguages.ts
new file mode 100644
index 0000000..f8e0cf7
--- /dev/null
+++ b/example/src/util/supportedLanguages.ts
@@ -0,0 +1,18 @@
+export const DEFAULT_LANG_OPTION = 'default';
+
+/** Lang values for PaymentSession.lang, matching iOS/Android SDK localizations. */
+export const SUPPORTED_LANG_OPTIONS = [
+  DEFAULT_LANG_OPTION,
+  'de',
+  'en',
+  'es',
+  'fr',
+  'ja',
+  'ko',
+  'pt-BR',
+  'pt-PT',
+  'ru',
+  'th',
+  'zh-Hans',
+  'zh-Hant',
+];
diff --git a/ios/AirwallexSdk+Session.swift b/ios/AirwallexSdk+Session.swift
index 27d9184..15dabfb 100644
--- a/ios/AirwallexSdk+Session.swift
+++ b/ios/AirwallexSdk+Session.swift
@@ -91,6 +91,9 @@ private extension AWXSession {
             }
         }
         countryCode = params["countryCode"] as! String
+        if let lang = params["lang"] as? String {
+            self.lang = lang
+        }
         if let returnUrl = params["returnUrl"] as? String {
             self.returnURL = returnUrl
         }
diff --git a/src/__tests__/index.test.tsx b/src/__tests__/index.test.tsx
index bf84291..ebf24e4 100644
--- a/src/__tests__/index.test.tsx
+++ b/src/__tests__/index.test.tsx
@@ -1 +1,17 @@
-it.todo('write a test');
+import type { OneOffSession } from '../types/PaymentSession';
+
+describe('PaymentSession', () => {
+  it('includes lang when provided', () => {
+    const session: OneOffSession = {
+      type: 'OneOff',
+      clientSecret: 'testSecret',
+      currency: 'HKD',
+      countryCode: 'HK',
+      lang: 'zh-Hans',
+      amount: 50,
+      paymentIntentId: 'intent123',
+    };
+
+    expect(session.lang).toBe('zh-Hans');
+  });
+});
diff --git a/src/types/PaymentSession.ts b/src/types/PaymentSession.ts
index a7599b5..43287de 100644
--- a/src/types/PaymentSession.ts
+++ b/src/types/PaymentSession.ts
@@ -10,6 +10,8 @@ interface BaseSession {
   isEmailRequired?: boolean;
   currency: string;
   countryCode: string;
+  /** Payment UI locale (e.g. `zh-Hans`, `pt-BR`). Omit for SDK default. */
+  lang?: string;
   amount: number;
   returnUrl?: string;
   googlePayOptions?: GooglePayOptions;