diff --git a/fluent-bundle/src/bundle.ts b/fluent-bundle/src/bundle.ts
index 59d7b81e..c6396e5c 100644
--- a/fluent-bundle/src/bundle.ts
+++ b/fluent-bundle/src/bundle.ts
@@ -4,6 +4,7 @@ import { FluentResource } from "./resource.js";
 import { FluentValue, FluentNone, FluentFunction } from "./types.js";
 import { Message, Term, Pattern } from "./ast.js";
 import { NUMBER, DATETIME } from "./builtins.js";
+import { getMemoizerForLocale, IntlCache } from "./memoizer.js";
 
 export type TextTransform = (text: string) => string;
 
@@ -22,12 +23,7 @@ export class FluentBundle {
   public _functions: Record<string, FluentFunction>;
   public _useIsolating: boolean;
   public _transform: TextTransform;
-  public _intls = new WeakMap<
-    | typeof Intl.NumberFormat
-    | typeof Intl.DateTimeFormat
-    | typeof Intl.PluralRules,
-    Record<string, Intl.NumberFormat | Intl.DateTimeFormat | Intl.PluralRules>
-  >();
+  public _intls: IntlCache;
 
   /**
    * Create an instance of `FluentBundle`.
@@ -78,6 +74,7 @@ export class FluentBundle {
     };
     this._useIsolating = useIsolating;
     this._transform = transform;
+    this._intls = getMemoizerForLocale(locales);
   }
 
   /**
diff --git a/fluent-bundle/src/memoizer.ts b/fluent-bundle/src/memoizer.ts
new file mode 100644
index 00000000..1f9bf204
--- /dev/null
+++ b/fluent-bundle/src/memoizer.ts
@@ -0,0 +1,19 @@
+export type IntlCache = Map<
+    | typeof Intl.NumberFormat
+    | typeof Intl.DateTimeFormat
+    | typeof Intl.PluralRules,
+    Record<string, Intl.NumberFormat | Intl.DateTimeFormat | Intl.PluralRules>
+  >;
+
+const cache = new Map<string, IntlCache>();
+
+export function getMemoizerForLocale(locales: string | string[]): IntlCache {
+  const stringLocale = Array.isArray(locales) ? locales.join(" ") : locales;
+  let memoizer = cache.get(stringLocale);
+  if (memoizer === undefined) {
+    memoizer = new Map();
+    cache.set(stringLocale, memoizer);
+  }
+
+  return memoizer;
+}
diff --git a/fluent-bundle/test/memoizer_test.js b/fluent-bundle/test/memoizer_test.js
new file mode 100644
index 00000000..ecf74e7d
--- /dev/null
+++ b/fluent-bundle/test/memoizer_test.js
@@ -0,0 +1,30 @@
+'use strict';
+
+import assert from 'assert';
+import {getMemoizerForLocale} from '../esm/memoizer.js';
+
+suite('Memoizer', function() {
+  test('returns same instance for same locale', function() {
+    const memoizer1 = getMemoizerForLocale('en')
+    const memoizer2 = getMemoizerForLocale('en')
+    assert.strictEqual(memoizer1, memoizer2)
+  });
+
+  test('returns different instance for different locale', function() {
+    const memoizer1 = getMemoizerForLocale('en')
+    const memoizer2 = getMemoizerForLocale('uk')
+    assert.notStrictEqual(memoizer1, memoizer2)
+  });
+
+  test('works with array of locales', function() {
+    const memoizer1 = getMemoizerForLocale(['en'])
+    const memoizer2 = getMemoizerForLocale(['en'])
+    assert.strictEqual(memoizer1, memoizer2)
+  });
+
+  test('works with string and array of locales', function() {
+    const memoizer1 = getMemoizerForLocale(['en'])
+    const memoizer2 = getMemoizerForLocale('en')
+    assert.strictEqual(memoizer1, memoizer2)
+  })
+})