chore: Move to Typescript (#2783)

This PR moves the entire project to Typescript. Due to the ~1000 ignores this will lead to a messy codebase for a while, but the churn is worth it – all of those ignore comments are places that were never type-safe previously.

closes #1282

shared/i18n/index.ts

@@ -0,0 +1,103 @@
+import i18n from "i18next";
+import backend from "i18next-http-backend";
+import { initReactI18next } from "react-i18next";
+
+// Note: Updating the available languages? Make sure to also update the
+// locales array in app/utils/i18n.js to enable translation for timestamps.
+export const languageOptions = [
+  {
+    label: "English (US)",
+    value: "en_US",
+  },
+  {
+    label: "简体中文 (Chinese, Simplified)",
+    value: "zh_CN",
+  },
+  {
+    label: "繁體中文 (Chinese, Traditional)",
+    value: "zh_TW",
+  },
+  {
+    label: "Deutsch (Deutschland)",
+    value: "de_DE",
+  },
+  {
+    label: "Español (España)",
+    value: "es_ES",
+  },
+  {
+    label: "فارسی (Persian)",
+    value: "fa_IR",
+  },
+  {
+    label: "Français (France)",
+    value: "fr_FR",
+  },
+  {
+    label: "Italiano (Italia)",
+    value: "it_IT",
+  },
+  {
+    label: "日本語 (Japanese)",
+    value: "ja_JP",
+  },
+  {
+    label: "한국어 (Korean)",
+    value: "ko_KR",
+  },
+  {
+    label: "Português (Brazil)",
+    value: "pt_BR",
+  },
+  {
+    label: "Português (Portugal)",
+    value: "pt_PT",
+  },
+  {
+    label: "Pусский (Россия)",
+    value: "ru_RU",
+  },
+  {
+    label: "Polskie (Polska)",
+    value: "pl_PL",
+  },
+];
+
+export const languages: string[] = languageOptions.map((i) => i.value);
+
+// Languages are stored in en_US format in the database, however the
+// frontend translation framework (i18next) expects en-US
+const underscoreToDash = (text: string) => text.replace("_", "-");
+
+const dashToUnderscore = (text: string) => text.replace("-", "_");
+
+export const initI18n = () => {
+  const lng = underscoreToDash(
+    // @ts-expect-error ts-migrate(2345) FIXME: Argument of type 'string | undefined' is not assig... Remove this comment to see the full error message
+    "DEFAULT_LANGUAGE" in process.env ? process.env.DEFAULT_LANGUAGE : "en_US"
+  );
+  i18n
+    .use(backend)
+    .use(initReactI18next)
+    .init({
+      backend: {
+        // this must match the path defined in routes. It's the path that the
+        // frontend UI code will hit to load missing translations.
+        loadPath: (languages: string[]) =>
+          `/locales/${dashToUnderscore(languages[0])}.json`,
+      },
+      interpolation: {
+        escapeValue: false,
+      },
+      react: {
+        useSuspense: false,
+      },
+      lng,
+      fallbackLng: lng,
+      supportedLngs: languages.map(underscoreToDash),
+      // Uncomment when debugging translation framework, otherwise it's noisy
+      // debug: process.env.NODE_ENV === "development",
+      keySeparator: false,
+    });
+  return i18n;
+};