feat(site): i18n string resolver with en fallback

site/src/i18n/ui.ts

@@ -0,0 +1,35 @@
+import en from "./en.json";
+import zhCN from "./zh-CN.json";
+import it from "./it.json";
+import fr from "./fr.json";
+import es from "./es.json";
+
+export const locales = ["en", "zh-CN", "it", "fr", "es"] as const;
+export type Locale = (typeof locales)[number];
+export const defaultLocale: Locale = "en";
+
+const dictionaries: Record<Locale, Record<string, string>> = {
+  en: en as Record<string, string>,
+  "zh-CN": zhCN as Record<string, string>,
+  it: it as Record<string, string>,
+  fr: fr as Record<string, string>,
+  es: es as Record<string, string>,
+};
+
+export function isLocale(value: string): value is Locale {
+  return (locales as readonly string[]).includes(value);
+}
+
+/** Resolve a translator for `locale`, falling back to en, then to the key. */
+export function useTranslations(locale: Locale) {
+  const dict = dictionaries[locale] ?? dictionaries[defaultLocale];
+  return (key: string, vars?: Record<string, string>): string => {
+    let value = dict[key] ?? dictionaries[defaultLocale][key] ?? key;
+    if (vars) {
+      for (const [k, v] of Object.entries(vars)) {
+        value = value.replaceAll(`{${k}}`, v);
+      }
+    }
+    return value;
+  };
+}