diff --git a/lighthouse-core/lib/i18n/i18n.js b/lighthouse-core/lib/i18n/i18n.js
index fea132ec615e..a7160013e649 100644
--- a/lighthouse-core/lib/i18n/i18n.js
+++ b/lighthouse-core/lib/i18n/i18n.js
@@ -21,22 +21,26 @@ const MESSAGE_INSTANCE_ID_REGEX = /(.* \| .*) # (\d+)$/;
 const MESSAGE_INSTANCE_ID_QUICK_REGEX = / # \d+$/;
 
 (() => {
-  // Node usually doesn't come with the locales we want built-in, so load the polyfill if we can.
+  // Node without full-icu doesn't come with the locales we want built-in. Load the polyfill if needed.
+  // See https://nodejs.org/api/intl.html#intl_options_for_building_node_js
 
-  try {
-    // @ts-ignore
-    const IntlPolyfill = require('intl');
-    // In browser environments where we don't need the polyfill, this won't exist
-    if (!IntlPolyfill.NumberFormat) return;
+  // Conditionally polyfills itself. Bundler removes this dep, so this will be a no-op in browsers.
+  // @ts-ignore
+  require('intl-pluralrules');
 
+  // @ts-ignore
+  const IntlPolyfill = require('intl');
+
+  // The bundler also removes this dep, so there's nothing to do if it's empty.
+  if (!IntlPolyfill.NumberFormat) return;
+
+  // Check if global implementation supports a minimum set of locales.
+  const minimumLocales = ['en', 'es', 'ru', 'zh'];
+  const supportedLocales = Intl.NumberFormat.supportedLocalesOf(minimumLocales);
+
+  if (supportedLocales.length !== minimumLocales.length) {
     Intl.NumberFormat = IntlPolyfill.NumberFormat;
     Intl.DateTimeFormat = IntlPolyfill.DateTimeFormat;
-
-    // Intl.PluralRules polyfilled on require().
-    // @ts-ignore
-    require('intl-pluralrules');
-  } catch (_) {
-    log.warn('i18n', 'Failed to install `intl` polyfill');
   }
 })();
 
diff --git a/lighthouse-core/report/html/renderer/util.js b/lighthouse-core/report/html/renderer/util.js
index 902cfc4cb68b..aa16df28a58e 100644
--- a/lighthouse-core/report/html/renderer/util.js
+++ b/lighthouse-core/report/html/renderer/util.js
@@ -192,7 +192,7 @@ class Util {
    */
   static formatNumber(number, granularity = 0.1) {
     const coarseValue = Math.round(number / granularity) * granularity;
-    return coarseValue.toLocaleString(Util.numberDateLocale);
+    return Util.numberFormatter.format(coarseValue);
   }
 
   /**
@@ -201,8 +201,7 @@ class Util {
    * @return {string}
    */
   static formatBytesToKB(size, granularity = 0.1) {
-    const kbs = (Math.round(size / 1024 / granularity) * granularity)
-      .toLocaleString(Util.numberDateLocale);
+    const kbs = Util.numberFormatter.format(Math.round(size / 1024 / granularity) * granularity);
     return `${kbs}${NBSP}KB`;
   }
 
@@ -213,7 +212,7 @@ class Util {
    */
   static formatMilliseconds(ms, granularity = 10) {
     const coarseTime = Math.round(ms / granularity) * granularity;
-    return `${coarseTime.toLocaleString(Util.numberDateLocale)}${NBSP}ms`;
+    return `${Util.numberFormatter.format(coarseTime)}${NBSP}ms`;
   }
 
   /**
@@ -223,7 +222,7 @@ class Util {
    */
   static formatSeconds(ms, granularity = 0.1) {
     const coarseTime = Math.round(ms / 1000 / granularity) * granularity;
-    return `${coarseTime.toLocaleString(Util.numberDateLocale)}${NBSP}s`;
+    return `${Util.numberFormatter.format(coarseTime)}${NBSP}s`;
   }
 
   /**
@@ -556,10 +555,11 @@ class Util {
    * @param {LH.Locale} locale
    */
   static setNumberDateLocale(locale) {
-    Util.numberDateLocale = locale;
-
     // When testing, use a locale with more exciting numeric formatting
-    if (Util.numberDateLocale === 'en-XA') Util.numberDateLocale = 'de';
+    if (locale === 'en-XA') locale = 'de';
+
+    Util.numberDateLocale = locale;
+    Util.numberFormatter = new Intl.NumberFormat(locale);
   }
 
   /**
@@ -618,6 +618,12 @@ class Util {
  */
 Util.numberDateLocale = 'en';
 
+/**
+ * This value stays in sync with Util.numberDateLocale.
+ * @type {Intl.NumberFormat}
+ */
+Util.numberFormatter = new Intl.NumberFormat(Util.numberDateLocale);
+
 /**
  * Report-renderer-specific strings.
  * @type {LH.I18NRendererStrings}
diff --git a/lighthouse-core/test/lib/i18n/swap-locale-test.js b/lighthouse-core/test/lib/i18n/swap-locale-test.js
index 9a73a7e8198a..289f405912cb 100644
--- a/lighthouse-core/test/lib/i18n/swap-locale-test.js
+++ b/lighthouse-core/test/lib/i18n/swap-locale-test.js
@@ -26,6 +26,12 @@ describe('swap-locale', () => {
     // Renderer formatted strings
     expect(lhrEn.i18n.rendererFormattedStrings.labDataTitle).toEqual('Lab Data');
     expect(lhrEs.i18n.rendererFormattedStrings.labDataTitle).toEqual('Datos de prueba');
+
+    // Formatted numbers in placeholders.
+    expect(lhrEn.audits['render-blocking-resources'].displayValue)
+      .toEqual('Potential savings of 1,130 ms');
+    expect(lhrEs.audits['render-blocking-resources'].displayValue)
+      .toEqual('Ahorro potencial de 1.130 ms');
   });
 
   it('can roundtrip back to english correctly', () => {
diff --git a/lighthouse-core/test/report/html/renderer/util-test.js b/lighthouse-core/test/report/html/renderer/util-test.js
index 774b64795b97..19009fe1af0e 100644
--- a/lighthouse-core/test/report/html/renderer/util-test.js
+++ b/lighthouse-core/test/report/html/renderer/util-test.js
@@ -9,6 +9,11 @@ const assert = require('assert');
 const Util = require('../../../../report/html/renderer/util.js');
 const sampleResult = require('../../../results/sample_v2.json');
 
+// Require i18n to make sure Intl is polyfilled in Node without full-icu for testing.
+// When Util is run in a browser, Intl will be supplied natively (IE11+).
+// eslint-disable-next-line no-unused-vars
+const i18n = require('../../../../lib/i18n/i18n.js');
+
 const NBSP = '\xa0';
 
 /* eslint-env jest */
@@ -47,25 +52,40 @@ describe('util helpers', () => {
     assert.equal(Util.formatDuration(28 * 60 * 60 * 1000 + 5000), `1${NBSP}d 4${NBSP}h 5${NBSP}s`);
   });
 
-  // TODO: need ICU support in node on Travis/Appveyor
-  it.skip('formats based on locale', () => {
+  it('formats numbers based on locale', () => {
+    // Requires full-icu or Intl polyfill.
     const number = 12346.858558;
 
     const originalLocale = Util.numberDateLocale;
     Util.setNumberDateLocale('de');
     assert.strictEqual(Util.formatNumber(number), '12.346,9');
-    Util.setNumberDateLocale(originalLocale); // reset
+    assert.strictEqual(Util.formatBytesToKB(number), `12,1${NBSP}KB`);
+    assert.strictEqual(Util.formatMilliseconds(number), `12.350${NBSP}ms`);
+    assert.strictEqual(Util.formatSeconds(number), `12,3${NBSP}s`);
+
+    Util.setNumberDateLocale(originalLocale); // reset locale
     assert.strictEqual(Util.formatNumber(number), '12,346.9');
+    assert.strictEqual(Util.formatBytesToKB(number), `12.1${NBSP}KB`);
+    assert.strictEqual(Util.formatMilliseconds(number), `12,350${NBSP}ms`);
+    assert.strictEqual(Util.formatSeconds(number), `12.3${NBSP}s`);
   });
 
-  it.skip('uses decimal comma with en-XA test locale', () => {
+  it('uses decimal comma with en-XA test locale', () => {
+    // Requires full-icu or Intl polyfill.
     const number = 12346.858558;
 
     const originalLocale = Util.numberDateLocale;
     Util.setNumberDateLocale('en-XA');
     assert.strictEqual(Util.formatNumber(number), '12.346,9');
-    Util.setNumberDateLocale(originalLocale); // reset
+    assert.strictEqual(Util.formatBytesToKB(number), `12,1${NBSP}KB`);
+    assert.strictEqual(Util.formatMilliseconds(number), `12.350${NBSP}ms`);
+    assert.strictEqual(Util.formatSeconds(number), `12,3${NBSP}s`);
+
+    Util.setNumberDateLocale(originalLocale); // reset locale
     assert.strictEqual(Util.formatNumber(number), '12,346.9');
+    assert.strictEqual(Util.formatBytesToKB(number), `12.1${NBSP}KB`);
+    assert.strictEqual(Util.formatMilliseconds(number), `12,350${NBSP}ms`);
+    assert.strictEqual(Util.formatSeconds(number), `12.3${NBSP}s`);
   });
 
   it('calculates a score ratings', () => {