Render the 404 error page in the composable i18n() handler when a route has no locale prefix

.changeset/dry-cars-joke.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes the composable `i18n()` handler from `astro/fetch` and `astro/hono` returning an empty 404 for paths without a locale prefix. It now renders the custom 404 page, matching `astro()`.

packages/astro/src/core/fetch/index.ts

@@ -11,7 +11,8 @@ import { FetchState as BaseFetchState } from './fetch-state.js';
 import type { AstroFetchState } from './fetch-state.js';
 export type { AstroFetchState };
 import { handleCache } from '../cache/handler.js';
-import { finalizeI18n, getI18n } from '../i18n/handler.js';
+import { handleI18nWithErrorFallback } from '../i18n/error-fallback.js';
+import { getI18n } from '../i18n/handler.js';
 import { getAmbientManifest } from '../manifest/ambient.js';
 import { handleMiddlewareWithErrorFallback } from '../middleware/astro-middleware.js';
 import { handlePagesWithErrorFallback } from '../pages/handler.js';
@@ -109,13 +110,14 @@ export function actions(state: FetchState): Promise<Response | undefined> | unde
 /**
  * Post-processes a response against the manifest's i18n configuration.
  * Handles locale redirects, 404s for invalid locales, and fallback
- * routing. Returns the response unmodified if i18n is not configured
- * (or the routing strategy is `manual`).
+ * routing. A null-body 404 produced for an invalid locale path renders
+ * the 404 error page. Returns the response unmodified if i18n is not
+ * configured (or the routing strategy is `manual`).
  */
 export function i18n(state: FetchState, response: Response): Promise<Response> {
 	const compiled = getI18n(state.manifest);
 	if (!compiled) return Promise.resolve(response);
-	return finalizeI18n(compiled, state, response);
+	return handleI18nWithErrorFallback(compiled, state, response);
 }
 
 /**

packages/astro/src/core/i18n/error-fallback.ts

@@ -0,0 +1,39 @@
+import { REROUTABLE_STATUS_CODES } from '../constants.js';
+import { renderErrorFromState } from '../errors/handler.js';
+import type { FetchState } from '../fetch/fetch-state.js';
+import { type CompiledI18n, finalizeI18n } from './handler.js';
+
+/**
+ * Runs {@link finalizeI18n} and, when it replaces the response with a
+ * null-body 404/500 (e.g. a locale-less path under `pathname-prefix-always`),
+ * renders the error page for it — the reroute `handleRequest` performs after
+ * `finalizeI18n` on the standard path. Responses passed through unchanged
+ * are returned as-is.
+ *
+ * Used by the composable `astro/fetch` `i18n()` entry point, where there is
+ * no surrounding `handleRequest` to supply this fallback. Kept out of
+ * `handler.ts` because that module is reachable from the client-importable
+ * `astro:i18n` virtual module, which must not pull in error-page rendering.
+ */
+export async function handleI18nWithErrorFallback(
+	compiled: CompiledI18n,
+	state: FetchState,
+	response: Response,
+): Promise<Response> {
+	const result = await finalizeI18n(compiled, state, response);
+	if (
+		result !== response &&
+		result.body === null &&
+		REROUTABLE_STATUS_CODES.includes(result.status) &&
+		!state.skipErrorReroute
+	) {
+		return renderErrorFromState(state, state.request, {
+			...state.renderOptions,
+			response: result,
+			status: result.status as 404 | 500,
+			error: result.status === 500 ? null : undefined,
+			pathname: state.pathname,
+		});
+	}
+	return result;
+}

packages/astro/test/units/hono/index.test.ts

@@ -3,7 +3,7 @@ import { describe, it } from 'node:test';
 import { Hono } from 'hono';
 import { FetchState } from '../../../dist/core/fetch/fetch-state.js';
 import { setAmbientManifest } from '../../../dist/core/manifest/ambient.js';
-import { astro, getFetchState } from '../../../dist/core/hono/index.js';
+import { astro, getFetchState, i18n, pages } from '../../../dist/core/hono/index.js';
 import { createComponent, render } from '../../../dist/runtime/server/index.js';
 import { createPage, createTestApp } from '../mocks.ts';
 
@@ -105,3 +105,36 @@ describe('getFetchState()', () => {
 		assert.match(await response.text(), /<h1>set via getFetchState<\/h1>/);
 	});
 });
+
+describe('i18n() Hono middleware', () => {
+	it('renders the custom 404 page for a path without a locale under pathname-prefix-always', async () => {
+		const notFoundPage = createComponent(() => render`<h1>Custom 404</h1>`);
+		const hono = createHonoApp(
+			createTestApp(
+				[
+					createPage(page, { route: '/' }),
+					createPage(page, { route: '/about' }),
+					createPage(notFoundPage, { route: '/404' }),
+				],
+				{
+					i18n: {
+						defaultLocale: 'en',
+						locales: ['en', 'fr'],
+						strategy: 'pathname-prefix-always',
+						fallbackType: 'rewrite',
+						fallback: undefined,
+						domains: {},
+						domainLookupTable: {},
+					},
+				},
+			),
+		);
+		hono.use(i18n());
+		hono.use(pages());
+
+		const response = await hono.fetch(new Request('http://example.com/about'));
+
+		assert.equal(response.status, 404);
+		assert.match(await response.text(), /<h1>Custom 404<\/h1>/);
+	});
+});