use submodule

excalidraw/excalidraw-app/app-language/language-detector.ts

@@ -0,0 +1,25 @@
+import { defaultLang, languages } from "@excalidraw/excalidraw";
+import LanguageDetector from "i18next-browser-languagedetector";
+
+export const languageDetector = new LanguageDetector();
+
+languageDetector.init({
+  languageUtils: {},
+});
+
+export const getPreferredLanguage = () => {
+  const detectedLanguages = languageDetector.detect();
+
+  const detectedLanguage = Array.isArray(detectedLanguages)
+    ? detectedLanguages[0]
+    : detectedLanguages;
+
+  const initialLanguage =
+    (detectedLanguage
+      ? // region code may not be defined if user uses generic preferred language
+        // (e.g. chinese vs instead of chinese-simplified)
+        languages.find((lang) => lang.code.startsWith(detectedLanguage))?.code
+      : null) || defaultLang.code;
+
+  return initialLanguage;
+};