i18n: Initialize FormatJS.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/i18n.js

@@ -1,10 +1,43 @@
 // For documentation on i18n in Zulip, see:
 // https://zulip.readthedocs.io/en/latest/translating/internationalization.html
 
+import {createIntl, createIntlCache} from "@formatjs/intl";
 import i18next from "i18next";
+import _ from "lodash";
 
 import {page_params} from "./page_params";
 
+const cache = createIntlCache();
+export const intl = createIntl(
+    {
+        locale: page_params.default_language,
+        defaultLocale: "en",
+        messages: page_params.translation_data,
+    },
+    cache,
+);
+
+export const $t = intl.formatMessage;
+
+export const default_html_elements = Object.fromEntries(
+    ["b", "code", "em", "i", "kbd", "p", "strong"].map((tag) => [
+        tag,
+        (content_html) => `<${tag}>${content_html}</${tag}>`,
+    ]),
+);
+
+export function $t_html(descriptor, values) {
+    return intl.formatMessage(descriptor, {
+        ...default_html_elements,
+        ...Object.fromEntries(
+            Object.entries(values ?? {}).map(([key, value]) => [
+                key,
+                typeof value === "function" ? value : _.escape(value),
+            ]),
+        ),
+    });
+}
+
 i18next.init({
     lng: "lang",
     resources: {