Add localization support and docs

src/hooks/useLanguage.js

@@ -0,0 +1,24 @@
+import React from 'react';
+import { translations, getInitialLanguage } from '../locales/index.js';
+
+export const useLanguage = () => {
+  const [currentLanguage, setCurrentLanguage] = React.useState(getInitialLanguage);
+
+  // Get current translations
+  const t = translations[currentLanguage] || translations.en;
+
+  // Change language and save to localStorage
+  const changeLanguage = (lang) => {
+    if (translations[lang]) {
+      setCurrentLanguage(lang);
+      localStorage.setItem('medPlanAssistant_language', lang);
+    }
+  };
+
+  return {
+    currentLanguage,
+    changeLanguage,
+    t,
+    availableLanguages: Object.keys(translations)
+  };
+};