diff --git a/assets/ts/settings-overlay.ts b/assets/ts/settings-overlay.ts
index b7f5566..cc1328b 100644
--- a/assets/ts/settings-overlay.ts
+++ b/assets/ts/settings-overlay.ts
@@ -89,8 +89,8 @@ export function initSettingsOverlay() {
   }
 
   const syncLanguage = (lang: string) => {
-    // Normalize language string
-    const isEn = lang.toLowerCase().startsWith('en_US');
+    // Normalize language string (html lang is hyphenated, e.g. "en-US")
+    const isEn = lang.toLowerCase().startsWith('en');
     const textAttr = isEn ? 'data-i18n-en' : 'data-i18n-zh';
     const ariaAttr = isEn ? 'data-i18n-aria-en' : 'data-i18n-aria-zh';
 
diff --git a/assets/ts/theme.ts b/assets/ts/theme.ts
index 74e4db0..8acb3d5 100644
--- a/assets/ts/theme.ts
+++ b/assets/ts/theme.ts
@@ -3,7 +3,7 @@
 
   // Polyfill translation lookup on client-side for dynamic updates
   // Since we don't have a JS i18n bundle, we'll derive translation from language
-  const isEn = window.location.pathname.startsWith('/en');
+  const isEn = window.location.pathname.startsWith('/en_US');
   
   const translations = {
     'zh_CN': {
diff --git a/internal/embedded/static/js/settings-overlay.js b/internal/embedded/static/js/settings-overlay.js
index 47938b3..21bbc46 100644
--- a/internal/embedded/static/js/settings-overlay.js
+++ b/internal/embedded/static/js/settings-overlay.js
@@ -136,7 +136,7 @@ function initSettingsOverlay() {
     updateClockCursorState();
   }
   const syncLanguage = (lang) => {
-    const isEn = lang.toLowerCase().startsWith("en_US");
+    const isEn = lang.toLowerCase().startsWith("en");
     const textAttr = isEn ? "data-i18n-en" : "data-i18n-zh";
     const ariaAttr = isEn ? "data-i18n-aria-en" : "data-i18n-aria-zh";
     document.body.querySelectorAll(`[${textAttr}]`).forEach((el) => {
diff --git a/internal/embedded/static/js/theme.js b/internal/embedded/static/js/theme.js
index 936d861..2dd1ca4 100644
--- a/internal/embedded/static/js/theme.js
+++ b/internal/embedded/static/js/theme.js
@@ -3,7 +3,7 @@
   // assets/ts/theme.ts
   (function() {
     const root = document.documentElement;
-    const isEn = window.location.pathname.startsWith("/en");
+    const isEn = window.location.pathname.startsWith("/en_US");
     const translations = {
       "zh_CN": {
         "theme.light": "\u6D45\u8272",
diff --git a/internal/embedded/templates/pages/note.html b/internal/embedded/templates/pages/note.html
index 5b2a94d..a8523b0 100644
--- a/internal/embedded/templates/pages/note.html
+++ b/internal/embedded/templates/pages/note.html
@@ -25,7 +25,7 @@
     <article class="note" data-has-mermaid="{{if .Note.HasMermaid}}true{{else}}false{{end}}" data-has-math="{{if .Note.HasMath}}true{{else}}false{{end}}">
       <header class="note-header">
         <div class="note-title-wrapper">
-          <a class="note-back-link" href="{{if eq .Lang "en_US"}}/en{{end}}/notes/" aria-label="{{T .Lang "action.back"}}">
+          <a class="note-back-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/notes/" aria-label="{{T .Lang "action.back"}}">
             <span class="material-symbol" aria-hidden="true">arrow_back</span>
           </a>
           <h1 class="note-title">
diff --git a/internal/embedded/templates/pages/tag.html b/internal/embedded/templates/pages/tag.html
index 17b4b1c..a6ba4d6 100644
--- a/internal/embedded/templates/pages/tag.html
+++ b/internal/embedded/templates/pages/tag.html
@@ -2,7 +2,7 @@
 <div class="notes-page">
   <section class="notes-list article-stage" aria-label="{{.PageTitle}}">
     <div class="tag-back-container">
-      <a class="tag-back-btn" aria-label="{{T .Lang "action.back"}}" href="{{if eq .Lang "en_US"}}/en{{end}}/notes/">
+      <a class="tag-back-btn" aria-label="{{T .Lang "action.back"}}" href="{{if eq .Lang "en_US"}}/en_US{{end}}/notes/">
         <span class="material-symbol" aria-hidden="true">arrow_back</span>
       </a>
       <h2 class="tag-back-title">{{.PageTitle}}</h2>
diff --git a/internal/embedded/templates/partials/header-nav.html b/internal/embedded/templates/partials/header-nav.html
index 4423301..aa9c0ac 100644
--- a/internal/embedded/templates/partials/header-nav.html
+++ b/internal/embedded/templates/partials/header-nav.html
@@ -1,23 +1,23 @@
 {{define "header_nav"}}
 <header class="site-header">
   <nav class="site-nav" aria-label="主导航">
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/">
       <span class="nav-icon material-symbol" aria-hidden="true">home</span>
       <span class="nav-label">{{T .Lang "nav.home"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/notes/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/notes/">
       <span class="nav-icon material-symbol" aria-hidden="true">article</span>
       <span class="nav-label">{{T .Lang "nav.notes"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/archive/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/archive/">
       <span class="nav-icon material-symbol" aria-hidden="true">archive</span>
       <span class="nav-label">{{T .Lang "nav.archive"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/graph/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/graph/">
       <span class="nav-icon material-symbol" aria-hidden="true">account_tree</span>
       <span class="nav-label">{{T .Lang "nav.graph"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/about/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/about/">
       <span class="nav-icon material-symbol" aria-hidden="true">info</span>
       <span class="nav-label">{{T .Lang "nav.about"}}</span>
     </a>
diff --git a/internal/embedded/templates/partials/mobile-drawer.html b/internal/embedded/templates/partials/mobile-drawer.html
index f467ff6..a826f7e 100644
--- a/internal/embedded/templates/partials/mobile-drawer.html
+++ b/internal/embedded/templates/partials/mobile-drawer.html
@@ -3,23 +3,23 @@
 <aside class="mobile-drawer" id="mobile-drawer" aria-label="移动端导航" aria-hidden="true">
   <div class="mobile-drawer-content">
     <nav class="mobile-drawer-nav" aria-label="主导航">
-      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/">
+      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/">
         <span class="material-symbol" aria-hidden="true">home</span>
         <span class="drawer-nav-label">{{T .Lang "nav.home"}}</span>
       </a>
-      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/notes/">
+      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/notes/">
         <span class="material-symbol" aria-hidden="true">article</span>
         <span class="drawer-nav-label">{{T .Lang "nav.notes"}}</span>
       </a>
-      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/archive/">
+      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/archive/">
         <span class="material-symbol" aria-hidden="true">archive</span>
         <span class="drawer-nav-label">{{T .Lang "nav.archive"}}</span>
       </a>
-      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/graph/">
+      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/graph/">
         <span class="material-symbol" aria-hidden="true">account_tree</span>
         <span class="drawer-nav-label">{{T .Lang "nav.graph"}}</span>
       </a>
-      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/about/">
+      <a class="drawer-nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/about/">
         <span class="material-symbol" aria-hidden="true">info</span>
         <span class="drawer-nav-label">{{T .Lang "nav.about"}}</span>
       </a>
diff --git a/internal/embedded/templates/partials/side-nav.html b/internal/embedded/templates/partials/side-nav.html
index 107c2c7..aa08812 100644
--- a/internal/embedded/templates/partials/side-nav.html
+++ b/internal/embedded/templates/partials/side-nav.html
@@ -9,23 +9,23 @@
   </a>
 
   <nav class="side-nav" aria-label="主导航" data-transition-region="side-nav">
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/">
       <span class="nav-icon material-symbol" aria-hidden="true">home</span>
       <span class="nav-label">{{T .Lang "nav.home"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/notes/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/notes/">
       <span class="nav-icon material-symbol" aria-hidden="true">article</span>
       <span class="nav-label">{{T .Lang "nav.notes"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/archive/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/archive/">
       <span class="nav-icon material-symbol" aria-hidden="true">archive</span>
       <span class="nav-label">{{T .Lang "nav.archive"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/graph/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/graph/">
       <span class="nav-icon material-symbol" aria-hidden="true">account_tree</span>
       <span class="nav-label">{{T .Lang "nav.graph"}}</span>
     </a>
-    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en{{end}}/about/">
+    <a class="nav-link" href="{{if eq .Lang "en_US"}}/en_US{{end}}/about/">
       <span class="nav-icon material-symbol" aria-hidden="true">info</span>
       <span class="nav-label">{{T .Lang "nav.about"}}</span>
     </a>
diff --git a/internal/render/render.go b/internal/render/render.go
index 47352fb..2cbaa13 100644
--- a/internal/render/render.go
+++ b/internal/render/render.go
@@ -793,7 +793,7 @@ func (r Renderer) render(outputPath, pageTemplate string, data any) error {
 		"tagURL": func(lang, tag string) template.URL {
 			prefix := ""
 			if lang == "en_US" {
-				prefix = "/en"
+				prefix = "/en_US"
 			}
 			return template.URL(prefix + "/tags/" + seo.TagSlug(tag) + "/")
 		},
diff --git a/internal/site/site.go b/internal/site/site.go
index cfcc6d5..4f49e77 100644
--- a/internal/site/site.go
+++ b/internal/site/site.go
@@ -393,7 +393,7 @@ func Build(options Options) (BuildResult, error) {
 					}
 					altPrefix := ""
 					if altL == "en_US" {
-						altPrefix = "/en"
+						altPrefix = "en_US"
 					}
 					noteAlternates = append(noteAlternates, seo.Alternate{
 						Lang: altL,
@@ -1187,7 +1187,7 @@ func collectTagLinksForLang(groups []*content.ArticleGroup, lang string, tagRegi
 
 	langPrefix := ""
 	if lang == "en_US" {
-		langPrefix = "/en"
+		langPrefix = "en_US"
 	}
 
 	links := make([]render.TagLink, 0, len(canonicalIDs))