diff --git a/docs/decisions/0017-performance-budgets-lighthouse-ci.md b/docs/decisions/0017-performance-budgets-lighthouse-ci.md
index 41183a0..5c45158 100644
--- a/docs/decisions/0017-performance-budgets-lighthouse-ci.md
+++ b/docs/decisions/0017-performance-budgets-lighthouse-ci.md
@@ -210,7 +210,7 @@ No browser-side RUM SDK in v1. The OTel browser tracing from [ADR-0012](0012-obs
 
 - `lighthouserc.js` exists at the repo root with the critical-routes list, the assertions matching the thresholds above, and a 3-iteration median configuration.
 - `apps/portal-shell/project.json` declares `budgets` with `maximumWarning == maximumError` (so an overshoot fails the build, matching `type: "error"` in spirit). Four entries: `initial` (≤ 1 MB raw), `anyScript` (≤ 300 KB raw), `anyComponentStyle` (≤ 6 KB raw, with 5 KB warning floor), `bundle name=styles` (≤ 150 KB raw). Angular CLI compares **raw** sizes; the values above are translated from the gzip-based ADR targets at the conventional ≈ 3× JS / ≈ 4× CSS compression ratios.
-- A complementary CI check in [`scripts/check-gzip-budgets.mjs`](../../scripts/check-gzip-budgets.mjs) (wired into `pnpm ci:perf` between the production build and Lighthouse) asserts the **actual** gzipped transfer size against the ADR thresholds: initial-JS-total ≤ 300 KB, any single lazy chunk ≤ 100 KB, total CSS ≤ 150 KB. Angular CLI does not natively support a gzip-mode budget — this script is the explicit gate. It parses `index.html` to distinguish initial assets from lazy chunks, gzips each file at level 9 (matching what HTTP servers typically serve), and exits non-zero on any breach.
+- A complementary CI check in [`scripts/check-gzip-budgets.mjs`](../../scripts/check-gzip-budgets.mjs) (wired into `pnpm ci:perf` between the production build and Lighthouse) asserts the **actual** gzipped transfer size against the ADR thresholds: initial-JS-total ≤ 300 KB, any single lazy chunk ≤ 100 KB, total CSS ≤ 150 KB. Angular CLI does not natively support a gzip-mode budget — this script is the explicit gate. It parses `index.html` to distinguish initial assets from lazy chunks, gzips each file at level 9 (matching what HTTP servers typically serve), and exits non-zero on any breach. The check is **per locale bundle** — `@angular/localize` (per [ADR-0019](0019-internationalisation-angular-localize.md)) emits one self-contained bundle under `dist/.../browser/<locale>/`, and each is what the user's browser actually downloads, so each is checked against the same budget independently. The script auto-detects locale-split vs flat layouts.
 - `package.json` exposes `ci:perf`, runnable locally with the same exit code as CI.
 - CI's `perf` gate from [ADR-0015](0015-cicd-gitea-actions.md) calls `pnpm ci:perf`. It is blocking on human PRs and on `push` to `main`; skipped on PRs authored by the Renovate bot user (`apf-portal-bot`) per the gating-policy subsection above.
 - `apps/portal-shell` exposes a Nx target `analyze` invoking `source-map-explorer` against the production build's source maps.
diff --git a/scripts/check-gzip-budgets.mjs b/scripts/check-gzip-budgets.mjs
index 3a44606..b0b8e06 100644
--- a/scripts/check-gzip-budgets.mjs
+++ b/scripts/check-gzip-budgets.mjs
@@ -19,11 +19,22 @@
  *    - sum of all CSS     ≤ BUDGET_CSS_TOTAL
  *    Exit non-zero on any violation.
  *
+ * Locale-split builds (ADR-0019)
+ * ------------------------------
+ * `@angular/localize` emits one self-contained bundle per locale under
+ * `dist/apps/portal-shell/browser/<locale>/`. The script auto-detects
+ * the layout: if the root has no `index.html` but immediate
+ * subdirectories do, each subdirectory is checked against the budgets
+ * separately. Budget thresholds apply *per locale* — each bundle is
+ * what the user's browser actually downloads. Violations across
+ * locales are aggregated and reported together so a single CI run
+ * surfaces every breach.
+ *
  * Invocation: `node scripts/check-gzip-budgets.mjs [dist-dir]`.
  * The default `dist-dir` is `dist/apps/portal-shell/browser`.
  */
 
-import { readdir, readFile } from 'node:fs/promises';
+import { readdir, readFile, stat } from 'node:fs/promises';
 import { gzipSync } from 'node:zlib';
 import { basename, join } from 'node:path';
 
@@ -36,22 +47,36 @@ const BUDGET_LAZY_JS_EACH = 100 * 1024;
 const BUDGET_CSS_TOTAL = 150 * 1024;
 
 const fmtKb = (n) => `${(n / 1024).toFixed(2)} KB`;
-
 const padFile = (s) => s.padEnd(36);
 
 async function gzipSize(path) {
   return gzipSync(await readFile(path), { level: 9 }).byteLength;
 }
 
-async function main() {
+async function fileExists(path) {
+  try {
+    await stat(path);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Check one Angular build directory (a single `index.html` and its
+ * sibling JS/CSS assets) against the ADR-0017 budgets. Returns the
+ * violations found — empty array means the bundle passed.
+ *
+ * The header passed in is rendered above the per-file table so the
+ * multi-locale invocation can prefix each section with the locale
+ * tag.
+ */
+async function checkBundle(bundleDir, header) {
   let indexHtml;
   try {
-    indexHtml = await readFile(join(dist, 'index.html'), 'utf8');
+    indexHtml = await readFile(join(bundleDir, 'index.html'), 'utf8');
   } catch (err) {
-    console.error(`✗ Could not read index.html under "${dist}".`);
-    console.error(`  Did you run "nx build portal-shell --configuration=production" first?`);
-    console.error(`  Underlying error: ${err.message}`);
-    process.exit(2);
+    throw new Error(`could not read ${join(bundleDir, 'index.html')}: ${err.message}`);
   }
 
   // Match every src=/href= that points at a .js or .css file in the
@@ -63,7 +88,7 @@ async function main() {
     ),
   );
 
-  const all = await readdir(dist);
+  const all = await readdir(bundleDir);
   const jsFiles = all.filter((f) => f.endsWith('.js'));
   const cssFiles = all.filter((f) => f.endsWith('.css'));
 
@@ -71,7 +96,7 @@ async function main() {
   const lazyJs = jsFiles.filter((f) => !referenced.has(f));
 
   const sized = async (files) =>
-    Promise.all(files.map(async (f) => ({ f, size: await gzipSize(join(dist, f)) })));
+    Promise.all(files.map(async (f) => ({ f, size: await gzipSize(join(bundleDir, f)) })));
 
   const initialJsSizes = await sized(initialJs);
   const lazyJsSizes = await sized(lazyJs);
@@ -83,20 +108,19 @@ async function main() {
 
   const violations = [];
 
-  console.log(`Gzip-transfer budget check (ADR-0017) — output: ${dist}\n`);
+  console.log(header);
 
   console.log('  Initial JS (loaded on first paint):');
   for (const { f, size } of initialJsSizes.sort((a, b) => b.size - a.size)) {
     console.log(`    ${padFile(f)} ${fmtKb(size)}`);
   }
-  const initialFlag =
-    totalInitialJs > BUDGET_INITIAL_JS_TOTAL ? ' ✗ EXCEEDS BUDGET' : ' ✓';
+  const initialFlag = totalInitialJs > BUDGET_INITIAL_JS_TOTAL ? ' ✗ EXCEEDS BUDGET' : ' ✓';
   console.log(
     `    ${padFile('TOTAL')} ${fmtKb(totalInitialJs)} / ${fmtKb(BUDGET_INITIAL_JS_TOTAL)}${initialFlag}`,
   );
   if (totalInitialJs > BUDGET_INITIAL_JS_TOTAL) {
     violations.push(
-      `initial JS total ${fmtKb(totalInitialJs)} > budget ${fmtKb(BUDGET_INITIAL_JS_TOTAL)}`,
+      `${header.trim()}: initial JS total ${fmtKb(totalInitialJs)} > budget ${fmtKb(BUDGET_INITIAL_JS_TOTAL)}`,
     );
   }
 
@@ -108,7 +132,9 @@ async function main() {
     const flag = size > BUDGET_LAZY_JS_EACH ? ' ✗ EXCEEDS BUDGET' : '';
     console.log(`    ${padFile(f)} ${fmtKb(size)}${flag}`);
     if (size > BUDGET_LAZY_JS_EACH) {
-      violations.push(`lazy chunk ${f} ${fmtKb(size)} > per-chunk budget ${fmtKb(BUDGET_LAZY_JS_EACH)}`);
+      violations.push(
+        `${header.trim()}: lazy chunk ${f} ${fmtKb(size)} > per-chunk budget ${fmtKb(BUDGET_LAZY_JS_EACH)}`,
+      );
     }
   }
   console.log(`    (per-chunk budget: ${fmtKb(BUDGET_LAZY_JS_EACH)})`);
@@ -119,19 +145,82 @@ async function main() {
   }
   const cssFlag = totalCss > BUDGET_CSS_TOTAL ? ' ✗ EXCEEDS BUDGET' : ' ✓';
   console.log(
-    `    ${padFile('TOTAL')} ${fmtKb(totalCss)} / ${fmtKb(BUDGET_CSS_TOTAL)}${cssFlag}`,
+    `    ${padFile('TOTAL')} ${fmtKb(totalCss)} / ${fmtKb(BUDGET_CSS_TOTAL)}${cssFlag}\n`,
   );
   if (totalCss > BUDGET_CSS_TOTAL) {
-    violations.push(`CSS total ${fmtKb(totalCss)} > budget ${fmtKb(BUDGET_CSS_TOTAL)}`);
+    violations.push(
+      `${header.trim()}: CSS total ${fmtKb(totalCss)} > budget ${fmtKb(BUDGET_CSS_TOTAL)}`,
+    );
+  }
+
+  return violations;
+}
+
+/**
+ * Resolve which directories to check. A locale-split build has no
+ * `index.html` at the root but does have one in each immediate
+ * subdirectory (ADR-0019 §"`@angular/localize` build-time mode").
+ * Returns either `[dist]` (flat layout) or `[dist/fr, dist/en, …]`
+ * (locale split, sorted alphabetically for deterministic output).
+ */
+async function resolveBundles(root) {
+  if (await fileExists(join(root, 'index.html'))) {
+    return [{ dir: root, label: root }];
+  }
+  let entries;
+  try {
+    entries = await readdir(root, { withFileTypes: true });
+  } catch (err) {
+    throw new Error(`could not read ${root}: ${err.message}`);
+  }
+  const subdirsWithIndex = [];
+  for (const entry of entries) {
+    if (!entry.isDirectory()) continue;
+    const candidate = join(root, entry.name);
+    if (await fileExists(join(candidate, 'index.html'))) {
+      subdirsWithIndex.push({ dir: candidate, label: entry.name });
+    }
+  }
+  if (subdirsWithIndex.length === 0) {
+    throw new Error(
+      `no index.html in ${root} and no locale subdirectory contains one — ` +
+        `did you run "nx build portal-shell --configuration=production" first?`,
+    );
+  }
+  subdirsWithIndex.sort((a, b) => a.label.localeCompare(b.label));
+  return subdirsWithIndex;
+}
+
+async function main() {
+  let bundles;
+  try {
+    bundles = await resolveBundles(dist);
+  } catch (err) {
+    console.error(`✗ ${err.message}`);
+    process.exit(2);
+  }
+
+  const multi = bundles.length > 1;
+  console.log(
+    `Gzip-transfer budget check (ADR-0017) — output: ${dist}` +
+      (multi ? ` (${bundles.length} locale bundles)` : '') +
+      '\n',
+  );
+
+  const violations = [];
+  for (const { dir, label } of bundles) {
+    const header = multi ? `[locale: ${label}]\n` : '';
+    const found = await checkBundle(dir, header);
+    violations.push(...found);
   }
 
   if (violations.length > 0) {
-    console.error('\n✗ ADR-0017 budget violations:');
+    console.error('✗ ADR-0017 budget violations:');
     for (const v of violations) console.error(`  - ${v}`);
     process.exit(1);
   }
 
-  console.log('\n✓ All ADR-0017 gzip-transfer budgets respected.');
+  console.log('✓ All ADR-0017 gzip-transfer budgets respected.');
 }
 
 main().catch((err) => {