diff --git a/messages/ja.json b/messages/jpn.json
similarity index 100%
rename from messages/ja.json
rename to messages/jpn.json
diff --git a/next.config.mjs b/next.config.mjs
index 56fe1f4..d94ad49 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -7,6 +7,14 @@ const withNextIntl = createNextIntlPlugin();
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   pageExtensions: ["ts", "tsx", "js", "jsx", "md", "mdx"],
+
+  redirects: async () => [
+    {
+      source: "/ja",
+      destination: "/jpn",
+      permanent: true,
+    },
+  ],
 };
 
 export default withMDX(withNextIntl(nextConfig));
diff --git a/src/api/translate.ts b/src/api/translate.ts
index 97d1a6d..b138185 100644
--- a/src/api/translate.ts
+++ b/src/api/translate.ts
@@ -40,7 +40,7 @@ export async function translate(
   const { source, target, dialect, pronoun, numReturnSequences = 1 } = params;
 
   let prompt: string = "";
-  if (source === "ja" && target === "ain") {
+  if (source === "jpn" && target === "ain") {
     prompt = `translate Japanese to Ainu (${dialect}, ${pronoun}): ${input}`;
   } else {
     prompt = `translate Ainu (${dialect}, ${pronoun}) to Japanese: ${input}`;
diff --git a/src/app/[locale]/_server.ts b/src/app/[locale]/_server.ts
index 3e4d19b..88f8b45 100644
--- a/src/app/[locale]/_server.ts
+++ b/src/app/[locale]/_server.ts
@@ -142,7 +142,7 @@ export async function fetchTranslation(
       transcriptions: {},
     };
 
-    if (source === "ja") {
+    if (source === "jpn") {
       result.transcriptions.translation = {
         type: "kana",
         text: to_kana(translation),
diff --git a/src/app/[locale]/about/ja.mdx b/src/app/[locale]/about/jpn.mdx
similarity index 100%
rename from src/app/[locale]/about/ja.mdx
rename to src/app/[locale]/about/jpn.mdx
diff --git a/src/app/[locale]/page.tsx b/src/app/[locale]/page.tsx
index 12d0456..f724033 100644
--- a/src/app/[locale]/page.tsx
+++ b/src/app/[locale]/page.tsx
@@ -47,7 +47,7 @@ export default async function Home(props: HomeProps) {
   setRequestLocale(params.locale);
 
   const text = searchParams?.text;
-  const source = searchParams?.source ?? "ja";
+  const source = searchParams?.source ?? "jpn";
   const target = searchParams?.target ?? "ain";
   const dialect = searchParams?.dialect ?? "沙流";
   const pronoun = searchParams?.pronoun ?? "first";
@@ -102,7 +102,7 @@ export default async function Home(props: HomeProps) {
           action={`/${params.locale}`}
           defaultValues={{
             text: text ?? "",
-            source: searchParams?.source ?? "ja",
+            source: searchParams?.source ?? "jpn",
             target: searchParams?.target ?? "ain",
             dialect,
             pronoun,
diff --git a/src/app/sitemap.ts b/src/app/sitemap.ts
index 400d3e2..a0494a2 100644
--- a/src/app/sitemap.ts
+++ b/src/app/sitemap.ts
@@ -3,7 +3,7 @@ import type { MetadataRoute } from "next";
 export default function sitemap(): MetadataRoute.Sitemap {
   return [
     {
-      url: "https://tunci.aynu.io/ja",
+      url: "https://tunci.aynu.io/jpn",
       lastModified: new Date(),
       alternates: {
         languages: {
@@ -12,7 +12,7 @@ export default function sitemap(): MetadataRoute.Sitemap {
       },
     },
     {
-      url: "https://tunci.aynu.io/ja/about",
+      url: "https://tunci.aynu.io/jpn/about",
       lastModified: new Date(),
       alternates: {
         languages: {
diff --git a/src/components/Composer/Composer.tsx b/src/components/Composer/Composer.tsx
index 68893dd..ca8d0c4 100644
--- a/src/components/Composer/Composer.tsx
+++ b/src/components/Composer/Composer.tsx
@@ -85,7 +85,7 @@ export const Composer: FC<ComposerProps> = (props) => {
 
   const handleChangeSource = (source: string): void => {
     setSource(source);
-    setTarget(source === "ja" ? "ain" : "ja");
+    setTarget(source === "jpn" ? "ain" : "jpn");
 
     if (translation && textareaRef.current && !dirty) {
       textareaRef.current.value = translation;
@@ -95,7 +95,7 @@ export const Composer: FC<ComposerProps> = (props) => {
 
   const handleChangeTarget = (target: string): void => {
     setTarget(target);
-    setSource(target === "ja" ? "ain" : "ja");
+    setSource(target === "jpn" ? "ain" : "jpn");
 
     if (translation && textareaRef.current && !dirty) {
       textareaRef.current.value = translation;
diff --git a/src/components/Composer/ComposerInput.tsx b/src/components/Composer/ComposerInput.tsx
index 90e7fe7..13e8e90 100644
--- a/src/components/Composer/ComposerInput.tsx
+++ b/src/components/Composer/ComposerInput.tsx
@@ -73,9 +73,9 @@ export const ComposerInput: FC<ComposerInputProps> = (props) => {
   const textareaLanguageRelatedAttributes: ComponentProps<
     typeof TextareaAutosize
   > = useMemo(() => {
-    if (source === "ja") {
+    if (source === "jpn") {
       return {
-        lang: "ja",
+        lang: "jpn",
       };
     }
 
diff --git a/src/components/Composer/LanguageSelector.tsx b/src/components/Composer/LanguageSelector.tsx
index d7c1672..015fa8d 100644
--- a/src/components/Composer/LanguageSelector.tsx
+++ b/src/components/Composer/LanguageSelector.tsx
@@ -28,7 +28,7 @@ export const LanguageSelector: FC<LanguageSelectorProps> = (props) => {
         aria-labelledby={id}
         onValueChange={onChange}
       >
-        <SegmentedControl.Item value="ja">
+        <SegmentedControl.Item value="jpn">
           {t("japanese")}
         </SegmentedControl.Item>
         <SegmentedControl.Item value="ain">{t("ainu")}</SegmentedControl.Item>
diff --git a/src/components/ContentInfo/ContentInfo.tsx b/src/components/ContentInfo/ContentInfo.tsx
index 1c187fa..05fec5d 100644
--- a/src/components/ContentInfo/ContentInfo.tsx
+++ b/src/components/ContentInfo/ContentInfo.tsx
@@ -27,13 +27,7 @@ export const ContentInfo: FC = async () => {
             <ul>
               <li>
                 <Link size="2" asChild>
-                  <NextLink
-                    rel="alternate"
-                    href="/ain-Latn"
-                    hrefLang="ain-Latn"
-                  >
-                    Aynu itak
-                  </NextLink>
+                  <NextLink href="/ain-Latn">Aynu itak</NextLink>
                 </Link>
               </li>
 
@@ -41,13 +35,7 @@ export const ContentInfo: FC = async () => {
 
               <li>
                 <Link size="2" asChild>
-                  <NextLink
-                    rel="alternate"
-                    href="/ain-Kana"
-                    hrefLang="ain-Kana"
-                  >
-                    アイヌイタㇰ
-                  </NextLink>
+                  <NextLink href="/ain-Kana">アイヌイタㇰ</NextLink>
                 </Link>
               </li>
 
@@ -55,9 +43,7 @@ export const ContentInfo: FC = async () => {
 
               <li>
                 <Link size="2" asChild>
-                  <NextLink rel="alternate" href="/ja" hrefLang="ja">
-                    日本語
-                  </NextLink>
+                  <NextLink href="/jpn">日本語</NextLink>
                 </Link>
               </li>
             </ul>
diff --git a/src/components/Entry/Entry.tsx b/src/components/Entry/Entry.tsx
index 32fdcfb..f943bae 100644
--- a/src/components/Entry/Entry.tsx
+++ b/src/components/Entry/Entry.tsx
@@ -46,7 +46,7 @@ const EntryRoot: React.FC<EntryRootProps> = (props) => {
           <blockquote lang="ain">{parse(textHTML)}</blockquote>
         </Text>
         <Text asChild>
-          <blockquote lang="ja">{parse(translationHTML)}</blockquote>
+          <blockquote lang="jpn">{parse(translationHTML)}</blockquote>
         </Text>
       </Flex>
 
diff --git a/src/i18n.ts b/src/i18n.ts
index 4528cd9..6012d9d 100644
--- a/src/i18n.ts
+++ b/src/i18n.ts
@@ -3,7 +3,7 @@ import { getRequestConfig } from "next-intl/server";
 import { routing } from "./i18n/routing";
 
 // Can be imported from a shared config
-export const locales = ["ain-Latn", "ain-Kana", "ja"];
+export const locales = ["ain-Latn", "ain-Kana", "jpn"];
 
 export default getRequestConfig(async ({ requestLocale }) => {
   let locale = await requestLocale;
diff --git a/src/i18n/routing.ts b/src/i18n/routing.ts
index ae4a52f..9c70617 100644
--- a/src/i18n/routing.ts
+++ b/src/i18n/routing.ts
@@ -2,7 +2,7 @@ import { createNavigation } from "next-intl/navigation";
 import { defineRouting } from "next-intl/routing";
 
 export const routing = defineRouting({
-  locales: ["ain-Latn", "ain-Kana", "ja"] as string[],
+  locales: ["ain-Latn", "ain-Kana", "jpn"] as string[],
   defaultLocale: "ain-Latn",
 });
 
diff --git a/src/middleware.ts b/src/middleware.ts
index b384800..e23dfaf 100644
--- a/src/middleware.ts
+++ b/src/middleware.ts
@@ -6,5 +6,5 @@ export default createMiddleware(routing);
 
 export const config = {
   // Match only internationalized pathnames
-  matcher: ["/", "/(ain-Latn|ain-Kana|ja)/:path*"],
+  matcher: ["/", "/(ain-Latn|ain-Kana|jpn)/:path*"],
 };