feat(core): Global lazy Intl polyfills and locale-sensitive date formatting

jest.config.js

@@ -4,8 +4,8 @@ const config = require("@patternslib/dev/jest.config.js");
 // config.setupFilesAfterEnv.push("./node_modules/@testing-library/jest-dom/extend-expect");
 config.setupFilesAfterEnv.push(path.resolve(__dirname, "./src/setup-tests.js"));
 config.transformIgnorePatterns = [
-    "/node_modules/(?!.pnpm/)(?!@patternslib/)(?!@plone/)(?!preact/)(?!screenfull/)(?!sinon/)(?!bootstrap/)(?!datatable/)(?!svelte/)(?!esm-env/).+\\.[t|j]sx?$",
-    "/node_modules/.pnpm/(?!@patternslib)(?!@plone)(?!preact)(?!screenfull)(?!sinon)(?!bootstrap)(?!datatable)(?!svelte)(?!esm-env)",
+    "/node_modules/(?!.pnpm/)(?!@patternslib/)(?!@plone/)(?!@formatjs/)(?!preact/)(?!screenfull/)(?!sinon/)(?!bootstrap/)(?!datatable/)(?!svelte/)(?!esm-env/).+\\.[t|j]sx?$",
+    "/node_modules/.pnpm/(?!@patternslib)(?!@plone)(?!@formatjs)(?!preact)(?!screenfull)(?!sinon)(?!bootstrap)(?!datatable)(?!svelte)(?!esm-env)",
 ];
 
 // Transforms. Order matters: Jest uses the first matching pattern, so the

package.json

@@ -12,6 +12,7 @@
     "packageManager": "pnpm@11.5.2+sha512.71c631e382066efc25625d5cf029075de07b61b37f6e27350fbd84b1bda5864c8c1967adc280776b45c30a715c0359a3be08fef42d5bb09e2b99029979692916",
     "dependencies": {
         "@11ty/eleventy-upgrade-help": "3.0.2",
+        "@formatjs/intl-datetimeformat": "^7.4.9",
         "@patternslib/pat-code-editor": "4.0.1",
         "@patternslib/patternslib": "9.10.6",
         "@plone/registry": "^2.7.2",

src/core/intl-loader.js

@@ -0,0 +1,49 @@
+/**
+ * Global Intl polyfill loader for Plone Mockup.
+ * Detects if the current browser supports the site's language and lazily
+ * loads the required polyfills and locale data if not.
+ */
+
+export async function ensureIntlSupport(lang) {
+    if (!lang) return;
+    const normalizedLang = lang.replace("_", "-");
+    const baseLang = normalizedLang.split("-")[0];
+
+    // Check if natively supported
+    try {
+        if (
+            typeof Intl !== "undefined" &&
+            Intl.DateTimeFormat &&
+            Intl.DateTimeFormat.supportedLocalesOf(normalizedLang).length > 0
+        ) {
+            return;
+        }
+    } catch {
+        // Fall through to loading polyfill if supportedLocalesOf fails
+    }
+
+    console.info(`Locale "${normalizedLang}" not supported. Loading polyfill...`);
+
+    // Load polyfill core if native support is missing for this locale.
+    try {
+        // Use polyfill-force to ensure we get a version that supports adding locale data,
+        // as native versions might not have the hooks for the locale-data files.
+        await import("@formatjs/intl-datetimeformat/polyfill-force.js");
+    } catch (e) {
+        console.error("Failed to load Intl polyfill core", e);
+    }
+
+    // Load specific locale data via Webpack dynamic chunk.
+    try {
+        // Use the package name with explicit .js extension.
+        // We have an alias in webpack.config.js to help resolve this path correctly
+        // without triggering package export warnings in Webpack 5.
+        await import(`@formatjs/intl-datetimeformat/locale-data/${baseLang}.js`);
+
+        if (Intl.DateTimeFormat.supportedLocalesOf(normalizedLang).length > 0) {
+            console.info(`Locale "${normalizedLang}" is now supported.`);
+        }
+    } catch (e) {
+        console.warn(`Could not load Intl data for ${baseLang}`, e);
+    }
+}

src/core/intl-loader.test.js

@@ -0,0 +1,70 @@
+import { ensureIntlSupport } from "./intl-loader";
+
+describe("intl-loader", () => {
+    let originalDateTimeFormat;
+
+    beforeAll(() => {
+        originalDateTimeFormat = Intl.DateTimeFormat;
+        jest.spyOn(console, "info").mockImplementation(() => {});
+        jest.spyOn(console, "warn").mockImplementation(() => {});
+        jest.spyOn(console, "error").mockImplementation(() => {});
+    });
+
+    afterAll(() => {
+        Intl.DateTimeFormat = originalDateTimeFormat;
+        console.info.mockRestore();
+        console.warn.mockRestore();
+        console.error.mockRestore();
+    });
+
+    beforeEach(() => {
+        jest.clearAllMocks();
+        // Reset to original before each test to have a clean state
+        // Note: some polyfill effects might persist if they touch other global objects
+        Intl.DateTimeFormat = originalDateTimeFormat;
+    });
+
+    it("should detect supported locales correctly", async () => {
+        // 'en' should be supported
+        await ensureIntlSupport("en");
+        expect(console.info).not.toHaveBeenCalledWith(expect.stringContaining("not supported"));
+    });
+
+    it("should handle locale normalization", async () => {
+        await ensureIntlSupport("pt_BR");
+        // pt-BR is likely supported, but we just check it doesn't crash
+    });
+
+    it("should load polyfill and provide Basque (eu) formatting", async () => {
+        // We force a mock that says 'eu' is NOT supported
+        const mockSupportedLocalesOf = jest.fn().mockImplementation((locales) => {
+            const l = Array.isArray(locales) ? locales[0] : locales;
+            if (l.startsWith('eu')) return [];
+            return originalDateTimeFormat.supportedLocalesOf(locales);
+        });
+
+        // We need to mock the property because it might be a getter
+        Object.defineProperty(Intl, 'DateTimeFormat', {
+            value: class extends originalDateTimeFormat {
+                static supportedLocalesOf = mockSupportedLocalesOf;
+            },
+            configurable: true
+        });
+
+        await ensureIntlSupport("eu");
+
+        expect(mockSupportedLocalesOf).toHaveBeenCalled();
+        expect(console.info).toHaveBeenCalledWith(expect.stringContaining("not supported"));
+
+        // After ensureIntlSupport, Intl.DateTimeFormat should have been replaced by the polyfill
+        // since we used polyfill-force.js (or at least it was called).
+
+        // Verify formatting using UTC to avoid timezone shifts
+        const date = new Date(Date.UTC(2020, 5, 1)); // June 1st UTC
+        const dtf = new Intl.DateTimeFormat("eu", { month: "short", timeZone: "UTC" });
+        const formatted = dtf.format(date);
+
+        // Basque short month for June is 'eka.'
+        expect(formatted.toLowerCase()).toContain("eka");
+    });
+});

src/pat/contentbrowser/src/ContentBrowser.svelte

@@ -1,9 +1,10 @@
 <script>
     import utils from "@patternslib/patternslib/src/core/utils";
-    import { getContext } from "svelte";
+    import { getContext, onMount } from "svelte";
     import * as animateScroll from "svelte-scrollto";
     import { fly } from "svelte/transition";
     import _t from "../../../core/i18n-wrapper";
+    import { ensureIntlSupport } from "../../../core/intl-loader";
     import Upload from "../../upload/upload";
     import contentStore from "./ContentStore";
     import {
@@ -472,6 +473,11 @@
         };
     }
 
+    onMount(async () => {
+        const lang = document.documentElement.lang || "en";
+        await ensureIntlSupport(lang);
+    });
+
     $effect(() => {
         if ($showContentBrowser) {
             contentItems.get({ path: $currentPath });

src/pat/filemanager/src/App.svelte

@@ -1,6 +1,8 @@
 <script>
     import { onMount, setContext } from "svelte";
     import logger from "@patternslib/patternslib/src/core/logging";
+    import { ensureIntlSupport } from "../../../core/intl-loader";
+    import { getLang } from "./utils/format.ts";
     import { ConfigStore } from "./stores/ConfigStore.svelte.ts";
     import { ContentsStore } from "./stores/ContentsStore.svelte.ts";
     import { ColumnsStore } from "./stores/ColumnsStore.svelte.ts";
@@ -118,6 +120,14 @@
 
     let isRestoringHistory = false;
 
+    // Lazily load Intl polyfills for the site language. Kept in its own
+    // async onMount so the listener-owning onMount below can stay synchronous
+    // and return its cleanup function (an async onMount returns a Promise,
+    // which Svelte ignores, leaking the listener).
+    onMount(async () => {
+        await ensureIntlSupport(getLang());
+    });
+
     onMount(() => {
         contents.load();
 

src/pat/filemanager/src/utils/format.ts

@@ -11,21 +11,27 @@ function parseDate(value: unknown): Date | null {
 }
 
 /** Detect the current UI language from the <html> tag, normalized for Intl. */
-function getLang(): string {
+export function getLang(): string {
     if (typeof document === "undefined") return "en";
     return (document.documentElement.lang || "en").replace("_", "-");
 }
 
 export function formatDate(value: unknown): string {
     const date = parseDate(value);
     if (!date) return "";
-    return new Intl.DateTimeFormat(getLang(), {
-        year: "numeric",
-        month: "short",
-        day: "numeric",
-        hour: "2-digit",
-        minute: "2-digit",
-    }).format(date);
+    const lang = getLang();
+    try {
+        return new Intl.DateTimeFormat(lang, {
+            year: "numeric",
+            month: "short",
+            day: "numeric",
+            hour: "2-digit",
+            minute: "2-digit",
+        }).format(date);
+    } catch (e) {
+        console.error(`Error formatting date for locale "${lang}":`, e);
+        return date.toLocaleString(); // Fallback
+    }
 }
 
 /**

src/pat/structure/structure.js

@@ -1,4 +1,5 @@
 import Base from "@patternslib/patternslib/src/core/base";
+import { ensureIntlSupport } from "../../core/intl-loader";
 
 export default Base.extend({
     name: "structure",
@@ -151,6 +152,8 @@ export default Base.extend({
         this.options.language =
             document.querySelector("html").getAttribute("lang") || "en";
 
+        await ensureIntlSupport(this.options.language);
+
         // the ``attributes`` options key is not compatible with backbone,
         // but queryHelper that will be constructed by the default
         // ResultCollection will expect this to be passed into it.

webpack.config.js

@@ -166,6 +166,13 @@ module.exports = () => {
         extensions: [".js", ".ts", ".json", ".wasm", ".svelte"],
         mainFields: ["browser", "module", "main"],
         conditionNames: ["svelte", "browser", "require"],
+        alias: {
+            ...config.resolve.alias,
+            "@formatjs/intl-datetimeformat/locale-data": path.resolve(
+                __dirname,
+                "node_modules/@formatjs/intl-datetimeformat/locale-data"
+            ),
+        },
     };
 
     // NOTE: above doesn't work.