fix: set checkout languageCode to ensure emails are sent in correct language

- Add CHECKOUT_LANGUAGE_CODE_UPDATE mutation to update checkout language
- Call language code update before completing checkout
- Language code (SR, EN, DE, FR) is now set on checkout before order creation
- This ensures order confirmation emails are sent in the customer's language
- Update step numbering in checkout flow (now 6 steps total)

src/lib/saleor/mutations/Checkout.ts

@@ -173,3 +173,40 @@ export const CHECKOUT_METADATA_UPDATE = gql`
     }
   }
 `;
+
+export const ORDER_METADATA_UPDATE = gql`
+  mutation OrderMetadataUpdate($orderId: ID!, $metadata: [MetadataInput!]!) {
+    updateMetadata(id: $orderId, input: $metadata) {
+      item {
+        ... on Order {
+          id
+          metadata {
+            key
+            value
+          }
+        }
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+`;
+
+export const CHECKOUT_LANGUAGE_CODE_UPDATE = gql`
+  mutation CheckoutLanguageCodeUpdate($checkoutId: ID!, $languageCode: LanguageCodeEnum!) {
+    checkoutLanguageCodeUpdate(checkoutId: $checkoutId, languageCode: $languageCode) {
+      checkout {
+        id
+        languageCode
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+`;