fix: validate language codes in URL path extraction (#634)

Author: wo-o29

fundamentals/today-i-learned/src/components/shared/layout/LayoutNavigation.tsx

@@ -2,18 +2,29 @@ import { useLocation } from "react-router-dom";
 import { OneNavigationReact } from "@shared/components";
 import { NavigationBar } from "./NavigationBar";
 
+const SUPPORTED_LANGUAGES = ["ko", "en", "ja", "zh-hans"];
+
+const extractLanguageCode = (path: string) => {
+  const firstSegment = path.split("/")[1];
+  const isValidLanguage = SUPPORTED_LANGUAGES.includes(firstSegment);
+
+  if (isValidLanguage) {
+    return firstSegment;
+  }
+
+  return null;
+};
+
 export const LayoutNavigation: React.FC = () => {
   const location = useLocation();
-  const isKorean =
-    !location.pathname.startsWith("/en") &&
-    !location.pathname.startsWith("/ja") &&
-    !location.pathname.startsWith("/zh-hans");
+  const lang = extractLanguageCode(location.pathname) ?? "ko";
+  const isKorean = lang === "ko";
 
   return (
     <>
       <NavigationBar />
       <OneNavigationReact
-        lang={location.pathname.split("/")[1] || "ko"}
+        lang={lang}
         isKorean={isKorean}
         pathname={location.pathname}
       />