diff --git a/internal/webapp/static/app.js b/internal/webapp/static/app.js
index a5bba2c..4ab75b3 100644
--- a/internal/webapp/static/app.js
+++ b/internal/webapp/static/app.js
@@ -518,6 +518,10 @@ if (!localStorage.getItem("tutor_lang")) {
 }
 
 updateStaticText();
+const savedLang = localStorage.getItem("tutor_lang") || document.documentElement.lang || "ko";
+document.querySelectorAll(".lang-btn").forEach((btn) => {
+  btn.classList.toggle("is-active", btn.dataset.lang === savedLang);
+});
 window.renderAuth = renderAuth;
 window.setLanguage = setLanguage;
 renderAuth();