feat: set checkout languageCode based on user locale

- Add languageCode to checkout store state
- Add setLanguageCode action to store
- Pass languageCode when creating checkout
- Header component sets language code from useLocale hook
- Enables multi-language order confirmation emails

src/components/layout/Header.tsx

@@ -5,7 +5,7 @@ import Link from "next/link";
 import Image from "next/image";
 import { usePathname } from "next/navigation";
 import { AnimatePresence, motion } from "framer-motion";
-import { useTranslations } from "next-intl";
+import { useTranslations, useLocale } from "next-intl";
 import { useSaleorCheckoutStore } from "@/stores/saleorCheckoutStore";
 import { User, ShoppingBag, Menu, X, Globe } from "lucide-react";
 import CartDrawer from "@/components/cart/CartDrawer";
@@ -16,14 +16,15 @@ interface HeaderProps {
   locale?: string;
 }
 
-export default function Header({ locale = "sr" }: HeaderProps) {
+export default function Header({ locale: propLocale = "sr" }: HeaderProps) {
   const t = useTranslations("Header");
   const pathname = usePathname();
   const dropdownRef = useRef<HTMLDivElement>(null);
   const [mobileMenuOpen, setMobileMenuOpen] = useState(false);
   const [scrolled, setScrolled] = useState(false);
   const [langDropdownOpen, setLangDropdownOpen] = useState(false);
-  const { getLineCount, toggleCart, initCheckout } = useSaleorCheckoutStore();
+  const { getLineCount, toggleCart, initCheckout, setLanguageCode } = useSaleorCheckoutStore();
+  const locale = useLocale();
 
   const itemCount = getLineCount();
   const currentLocale = isValidLocale(locale) ? LOCALE_CONFIG[locale] : LOCALE_CONFIG.sr;
@@ -58,6 +59,13 @@ export default function Header({ locale = "sr" }: HeaderProps) {
     initCheckout();
   }, [initCheckout]);
 
+  // Set language code for checkout based on current locale
+  useEffect(() => {
+    if (locale) {
+      setLanguageCode(locale);
+    }
+  }, [locale, setLanguageCode]);
+
   useEffect(() => {
     const handleScroll = () => {
       setScrolled(window.scrollY > 50);