diff --git a/src/app/sitemap.ts b/src/app/sitemap.ts
index fcce47f3..2783b8c7 100644
--- a/src/app/sitemap.ts
+++ b/src/app/sitemap.ts
@@ -6,14 +6,35 @@ export default function sitemap(): MetadataRoute.Sitemap {
     {
       url: BASE_URL,
       lastModified: new Date(),
+      alternates: {
+        languages: {
+          en: `${BASE_URL}/`,
+          ja: `${BASE_URL}/ja/`,
+          "x-default": `${BASE_URL}/`,
+        },
+      },
     },
     {
       url: `${BASE_URL}/introduction`,
       lastModified: new Date(),
+      alternates: {
+        languages: {
+          en: `${BASE_URL}/introduction`,
+          ja: `${BASE_URL}/ja/introduction`,
+          "x-default": `${BASE_URL}/introduction`,
+        },
+      },
     },
     {
       url: `${BASE_URL}/libraries`,
       lastModified: new Date(),
+      alternates: {
+        languages: {
+          en: `${BASE_URL}/libraries`,
+          ja: `${BASE_URL}/ja/libraries`,
+          "x-default": `${BASE_URL}/libraries`,
+        },
+      },
     },
   ];
 }