Move hamburger to right, fix nav overflow, add auto language detection

src/i18n/request.ts

@@ -1,9 +1,8 @@
-import { cookies } from "next/headers";
+import { cookies, headers } from "next/headers";
 import { getRequestConfig } from "next-intl/server";
 
-// i18n WITHOUT routing: the locale is chosen by a `NEXT_LOCALE` cookie (set by
-// the language switcher) rather than a URL segment, so every existing route and
-// the access-guard middleware keep working unchanged. English is the fallback.
+// i18n WITHOUT routing: the locale is chosen by a `NEXT_LOCALE` cookie, then
+// the Accept-Language header, and finally English as fallback.
 export const SUPPORTED_LOCALES = ["en", "it", "nl", "de", "fr", "es", "pt", "pl", "sv", "tr", "ro", "hu", "cs", "sk", "da", "no", "el", "bg", "hr", "sr", "uk", "ru"] as const;
 export type AppLocale = (typeof SUPPORTED_LOCALES)[number];
 export const DEFAULT_LOCALE: AppLocale = "en";
@@ -12,10 +11,37 @@ export function isSupportedLocale(value: string | undefined): value is AppLocale
   return !!value && (SUPPORTED_LOCALES as readonly string[]).includes(value);
 }
 
+function detectLocaleFromAcceptLanguage(acceptLanguage: string | null): AppLocale | null {
+  if (!acceptLanguage) return null;
+  const locales = acceptLanguage
+    .split(",")
+    .map((entry) => {
+      const [tag, qPart] = entry.split(";");
+      const quality = qPart ? parseFloat(qPart.replace("q=", "")) : 1;
+      const lang = tag?.trim().split("-")[0] ?? "";
+      return { lang, quality };
+    })
+    .filter((l) => l.lang)
+    .sort((a, b) => b.quality - a.quality);
+
+  for (const { lang } of locales) {
+    if (isSupportedLocale(lang)) return lang;
+  }
+  return null;
+}
+
 export default getRequestConfig(async () => {
   const store = await cookies();
   const cookieLocale = store.get("NEXT_LOCALE")?.value;
-  const locale: AppLocale = isSupportedLocale(cookieLocale) ? cookieLocale : DEFAULT_LOCALE;
+
+  let locale: AppLocale;
+  if (isSupportedLocale(cookieLocale)) {
+    locale = cookieLocale;
+  } else {
+    const headersList = await headers();
+    const detected = detectLocaleFromAcceptLanguage(headersList.get("Accept-Language"));
+    locale = detected ?? DEFAULT_LOCALE;
+  }
 
   // Safe: `locale` is validated against SUPPORTED_LOCALES above (only en/it/nl/de/fr/es).
   const messages = (await import(`../messages/${locale}.json`)).default;