feat: add internationalization message platform

tests/component/async-surface.test.jsx

@@ -50,7 +50,9 @@ describe("async UI state matrix", () => {
     render(<AsyncSurface state={state}>existing content</AsyncSurface>);
 
     expect(screen.getByText("existing content")).toBeVisible();
-    expect(screen.getByRole("status")).toHaveTextContent("refreshing");
+    expect(screen.getByRole("status")).toHaveTextContent(
+      "최신 정보를 확인하고 있습니다.",
+    );
   });
 
   it("connects stale retry and conflict resolution to real callbacks", async () => {

tests/component/chunk-recovery-boundary.test.tsx

@@ -60,7 +60,9 @@ describe("chunk recovery boundary classification", () => {
       </FeatureBoundary>,
     );
 
-    expect(screen.getByRole("alert")).toHaveTextContent("error.render_failure");
+    expect(screen.getByRole("alert")).toHaveTextContent(
+      "화면을 표시하지 못했습니다.",
+    );
     expect(recover).not.toHaveBeenCalled();
   });
 });

tests/component/design-system-platform.test.tsx

@@ -189,7 +189,7 @@ describe("design-system platform interactions", () => {
     await user.click(screen.getByRole("button", { name: "중복" }));
     expect(screen.getByText("×2")).toBeVisible();
     await user.click(screen.getByRole("button", { name: "다섯 개" }));
-    const region = screen.getByRole("region", { name: "Notifications" });
+    const region = screen.getByRole("region", { name: "알림" });
     expect(within(region).getAllByRole("article")).toHaveLength(3);
     expect(within(region).queryByText("알림 0")).not.toBeInTheDocument();
     expect(within(region).getByText("알림 4")).toBeVisible();

tests/component/locale-platform.test.tsx

@@ -0,0 +1,120 @@
+// @vitest-environment jsdom
+
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { useState } from "react";
+import { describe, expect, it } from "vitest";
+
+import {
+  Button,
+  Drawer,
+  Pagination,
+  Tabs,
+} from "../../src/presentation/design-system/index.js";
+import {
+  LocaleProvider,
+  useLocale,
+  type SupportedLocale,
+} from "../../src/presentation/i18n/index.js";
+
+function LocaleHarness() {
+  const { direction, locale, message, setLocale } = useLocale();
+  const [drawerOpen, setDrawerOpen] = useState(false);
+  return (
+    <>
+      <label htmlFor="test-locale">{message("shell.locale")}</label>
+      <select
+        id="test-locale"
+        onChange={(event) =>
+          setLocale(event.currentTarget.value as SupportedLocale)
+        }
+        value={locale}
+      >
+        <option value="ko-KR">한국어</option>
+        <option value="en-US">English</option>
+        <option value="ar-EG">RTL</option>
+      </select>
+      <output>{`${locale}:${direction}`}</output>
+      <Button onClick={() => setDrawerOpen(true)}>
+        {message("shell.menu")}
+      </Button>
+      <Drawer
+        closeLabel={message("shell.closeMenu")}
+        onClose={() => setDrawerOpen(false)}
+        open={drawerOpen}
+        title={message("shell.menu")}
+      >
+        content
+      </Drawer>
+    </>
+  );
+}
+
+describe("locale provider runtime", () => {
+  it("switches copy and synchronizes the document language and direction", async () => {
+    const user = userEvent.setup();
+    render(
+      <LocaleProvider>
+        <LocaleHarness />
+      </LocaleProvider>,
+    );
+
+    expect(document.documentElement).toHaveAttribute("lang", "ko-KR");
+    await user.selectOptions(screen.getByLabelText("언어"), "en-US");
+    expect(screen.getByLabelText("Language")).toHaveValue("en-US");
+    expect(document.documentElement).toHaveAttribute("lang", "en-US");
+    expect(document.documentElement).toHaveAttribute("dir", "ltr");
+
+    await user.selectOptions(screen.getByLabelText("Language"), "ar-EG");
+    expect(document.documentElement).toHaveAttribute("lang", "ar-EG");
+    expect(document.documentElement).toHaveAttribute("dir", "rtl");
+    await user.click(screen.getByRole("button", { name: "Menu" }));
+    expect(screen.getByRole("dialog", { name: "Menu" })).toHaveAttribute(
+      "open",
+    );
+  });
+
+  it("reverses horizontal tab focus semantics in RTL", async () => {
+    const user = userEvent.setup();
+    render(
+      <LocaleProvider initialLocale="ar-EG">
+        <Tabs
+          activation="manual"
+          label="sections"
+          tabs={[
+            { id: "one", label: "One", panel: "One panel" },
+            { id: "two", label: "Two", panel: "Two panel" },
+            { id: "three", label: "Three", panel: "Three panel" },
+          ]}
+        />
+      </LocaleProvider>,
+    );
+    const first = screen.getByRole("tab", { name: "One" });
+    first.focus();
+    await user.keyboard("{ArrowRight}");
+    expect(screen.getByRole("tab", { name: "Three" })).toHaveFocus();
+    await user.keyboard("{ArrowLeft}");
+    expect(first).toHaveFocus();
+  });
+
+  it("keeps pagination semantics while direction-aware icons remain decorative", () => {
+    render(
+      <LocaleProvider initialLocale="ar-EG">
+        <Pagination
+          label="pages"
+          nextLabel="Next page"
+          onChange={() => {}}
+          page={2}
+          pageCount={3}
+          pageLabel={(page) => `Page ${page}`}
+          previousLabel="Previous page"
+        />
+      </LocaleProvider>,
+    );
+    expect(
+      screen.getByRole("button", { name: "Previous page" }),
+    ).toBeEnabled();
+    expect(screen.getByRole("button", { name: "Next page" })).toBeEnabled();
+    expect(screen.queryByRole("img")).not.toBeInTheDocument();
+  });
+});

tests/component/page-templates.test.tsx

@@ -86,7 +86,7 @@ describe("page template slot contracts", () => {
       />,
     );
     expect(screen.getByRole("heading", { level: 1, name: "Offline" })).toBeVisible();
-    expect(screen.getByText("SAFE-123")).toBeVisible();
+    expect(screen.getByText(/SAFE-123/)).toBeVisible();
     expect(document.body).not.toHaveTextContent("stack");
   });
 });

tests/component/render-boundary.test.jsx

@@ -28,7 +28,9 @@ describe("render recovery boundaries", () => {
       </FeatureBoundary>,
     );
 
-    expect(screen.getByRole("alert")).toHaveTextContent("error.render_failure");
+    expect(screen.getByRole("alert")).toHaveTextContent(
+      "화면을 표시하지 못했습니다.",
+    );
     expect(onRenderFailure).toHaveBeenCalledWith({
       routeId: "APP_HOME",
       buildId: "build-a",
@@ -83,7 +85,7 @@ describe("render recovery boundaries", () => {
       </FeatureBoundary>,
     );
     shouldThrow = false;
-    await user.click(screen.getByRole("button", { name: "retry" }));
+    await user.click(screen.getByRole("button", { name: "다시 시도" }));
     view.rerender(
       <FeatureBoundary routeId="APP_HOME" buildId="build-a">
         <Recoverable />