diff --git a/pages/api/auth/[...nextauth].js b/pages/api/auth/[...nextauth].js
index 09ffa396..4c4534c3 100644
--- a/pages/api/auth/[...nextauth].js
+++ b/pages/api/auth/[...nextauth].js
@@ -37,12 +37,12 @@ const appendParamsAndPathToNewUrl = (fromUrl, toUrl) => {
     return toUrlObj.toString();
 };
 
-const resolveRequestLocale = (req) => {
-    const locale =
-        req?.body?.locale || req?.query?.locale || req?.cookies?.pedw_locale;
+// const resolveRequestLocale = (req) => {
+//     const locale =
+//         req?.body?.locale || req?.query?.locale || req?.cookies?.pedw_locale;
 
-    return locale === "cy" ? "cy" : "en";
-};
+//     return locale === "cy" ? "cy" : "en";
+// };
 
 const resolveCrmLocale = async (email) => {
     if (!email) return null;
@@ -94,6 +94,44 @@ const buildLocalizedVerificationUrl = ({ url, email, effectiveLocale }) => {
     return appendParamsAndPathToNewUrl(url, newURL);
 };
 
+const getLocaleFromCallbackUrl = (callbackUrl) => {
+    if (!callbackUrl) return null;
+
+    try {
+        const parsed = new URL(callbackUrl);
+        const locale = parsed.searchParams.get("locale");
+
+        if (locale === "cy" || parsed.pathname.startsWith("/cy")) {
+            return "cy";
+        }
+
+        if (locale === "en") {
+            return "en";
+        }
+
+        return null;
+    } catch {
+        return null;
+    }
+};
+
+const resolveRequestLocale = (req) => {
+    const directLocale =
+        req?.body?.locale || req?.query?.locale || req?.cookies?.pedw_locale;
+
+    if (directLocale === "cy") return "cy";
+    if (directLocale === "en") return "en";
+
+    const callbackLocale =
+        getLocaleFromCallbackUrl(req?.body?.callbackUrl) ||
+        getLocaleFromCallbackUrl(req?.query?.callbackUrl) ||
+        getLocaleFromCallbackUrl(
+            req?.cookies?.["__Secure-next-auth.callback-url"]
+        );
+
+    return callbackLocale === "cy" ? "cy" : "en";
+};
+
 const authOptions = (req, res) => {
     const requestLocale = resolveRequestLocale(req);