diff --git a/js/common/NumberPairsQueryParameters.ts b/js/common/NumberPairsQueryParameters.ts
index 8615a70..d26cda9 100644
--- a/js/common/NumberPairsQueryParameters.ts
+++ b/js/common/NumberPairsQueryParameters.ts
@@ -11,8 +11,15 @@ import logGlobal from '../../../phet-core/js/logGlobal.js';
 import numberPairs from '../numberPairs.js';
 
 const SCHEMA_MAP = {
-  //TODO add schemas for query parameters
-};
+
+  // Specifies a second locale for the speech synthesis feature.
+  // Values are a locale code, e.g. "en" or "zh_CN". null means no second locale.
+  secondLocale: {
+    public: true,
+    type: 'string',
+    defaultValue: null
+  }
+} as const;
 
 const NumberPairsQueryParameters = QueryStringMachine.getAll( SCHEMA_MAP );
 
diff --git a/js/common/model/NumberPairsPreferences.ts b/js/common/model/NumberPairsPreferences.ts
new file mode 100644
index 0000000..487c97b
--- /dev/null
+++ b/js/common/model/NumberPairsPreferences.ts
@@ -0,0 +1,61 @@
+// Copyright 2024, University of Colorado Boulder
+
+/**
+ * NumberPairsPreferences is the model for sim-specific preferences, accessed via the Preferences dialog.
+ * These preferences are global, affect all screens, and are not affected by 'reset all'.
+ *
+ * @author Chris Malley (PixelZoom, Inc.)
+ */
+
+import numberPairs from '../../numberPairs.js';
+import BooleanProperty from '../../../../axon/js/BooleanProperty.js';
+import localeProperty, { Locale, LocaleProperty } from '../../../../joist/js/i18n/localeProperty.js';
+import Property from '../../../../axon/js/Property.js';
+import DerivedProperty from '../../../../axon/js/DerivedProperty.js';
+import NumberPairsQueryParameters from '../NumberPairsQueryParameters.js';
+import Tandem from '../../../../tandem/js/Tandem.js';
+
+//TODO https://github.com/phetsims/number-pairs/issues/22 second or secondary? Other sims in the suite are very inconsistent.
+
+// As with the primary locale, use initialize-globals checkAndRemapLocale() to check validity of the second locale.
+// This potentially either falls back to 'en', or remaps from 3-character locales to PhET locales.
+let secondLocale = NumberPairsQueryParameters.secondLocale;
+if ( secondLocale !== null ) {
+  const remappedLocale = phet.chipper.remapLocale( secondLocale, false );
+  secondLocale = phet.chipper.getValidRuntimeLocale( remappedLocale );
+}
+
+const secondLocaleProperty = new LocaleProperty( secondLocale as Locale || localeProperty.value, {
+  tandem: Tandem.PREFERENCES.createTandem( 'secondLocaleProperty' ),
+  phetioFeatured: true
+} );
+
+const NumberPairsPreferences = {
+
+  // second locale
+  secondLocaleProperty: secondLocaleProperty,
+
+  // voice of the primary locale
+  //TODO https://github.com/phetsims/number-pairs/issues/22 Cannot instrument because there is no IOType for SpeechSynthesisVoice.
+  primaryVoiceProperty: new Property<SpeechSynthesisVoice | null>( null ),
+
+  // voice of the second locale
+  //TODO https://github.com/phetsims/number-pairs/issues/22 Cannot instrument because there is no IOType for SpeechSynthesisVoice.
+  secondVoiceProperty: new Property<SpeechSynthesisVoice | null>( null ),
+
+  //TODO https://github.com/phetsims/number-pairs/issues/22 Properties below here are global, but do not belong in Preferences.
+
+  // If a valid secondary locale was provided via a query parameter, display the secondary locale on sim startup.
+  showSecondLocaleProperty: new BooleanProperty( !!NumberPairsQueryParameters.secondLocale ),
+
+  // Whether the sim is using its primary locale or secondary locale on screens that support two locales.
+  isPrimaryLocaleProperty: new BooleanProperty( true ),
+
+  // Strings for the current secondLocale.
+  secondLocaleStringsProperty: new DerivedProperty( [ secondLocaleProperty ], secondLocale => {
+    return phet.chipper.strings[ secondLocale ];
+  } )
+};
+
+numberPairs.register( 'NumberPairsPreferences', NumberPairsPreferences );
+export default NumberPairsPreferences;
\ No newline at end of file