diff --git a/src/main.tsx b/src/main.tsx
index 15271f9..fb24bd5 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -1,10 +1,29 @@
 import { render } from "preact";
 import { App } from "./app";
-import { useState } from "preact/hooks";
+import { useState, useEffect } from "preact/hooks";
 import { Tr, langCodeContext, LANG_OPTIONS } from "./translate";
 
 function Base() {
   const [langCode, setLangCode] = useState("en-US");
+
+  // select language
+  useEffect(() => {
+    const browserCode = window.navigator.language;
+    for (const key in LANG_OPTIONS) {
+      for (const i in LANG_OPTIONS[key].matches) {
+        const code = LANG_OPTIONS[key].matches[i];
+        if (code === browserCode) {
+          console.log(`set langCode to "${code}"`);
+          setLangCode(key);
+          return;
+        }
+      }
+    }
+    // fallback to english
+    console.log('fallback langCode to "en-US"');
+    setLangCode("en-US");
+  }, []);
+
   return (
     /* @ts-ignore */
     <langCodeContext.Provider value={{ langCode, setLangCode }}>