Add Redux and reducers.

Load i18n files and add dayjs.

src/redux/reducers/locale.ts

@@ -0,0 +1,50 @@
+import { Language } from "../../context/Locale";
+import { SyncData, SyncKeys, SyncUpdateAction } from "./sync";
+
+export type LocaleAction =
+    | { type: undefined }
+    | {
+          type: "SET_LOCALE";
+          locale: Language;
+      }
+    | SyncUpdateAction;
+
+export function findLanguage(lang?: string): Language {
+    if (!lang) {
+        if (typeof navigator === "undefined") {
+            lang = Language.ENGLISH;
+        } else {
+            lang = navigator.language;
+        }
+    }
+
+    const code = lang.replace("-", "_");
+
+    const short = code.split("_")[0];
+    for (const key of Object.keys(Language)) {
+        const value = (Language as any)[key];
+        if (value.startsWith(code)) {
+            return value;
+        }
+    }
+
+    for (const key of Object.keys(Language).reverse()) {
+        const value = (Language as any)[key];
+        if (value.startsWith(short)) {
+            return value;
+        }
+    }
+
+    return Language.ENGLISH;
+}
+
+export function locale(state = findLanguage(), action: LocaleAction): Language {
+    switch (action.type) {
+        case "SET_LOCALE":
+            return action.locale;
+        case "SYNC_UPDATE":
+            return (action.update.locale?.[1] ?? state) as Language;
+        default:
+            return state;
+    }
+}