diff --git a/js/LocalizedString.ts b/js/LocalizedString.ts
index 570e3a957..168f58497 100644
--- a/js/LocalizedString.ts
+++ b/js/LocalizedString.ts
@@ -27,7 +27,7 @@ export type LocalizedStringStateDelta = Partial<Record<Locale, TranslationString
 export type StringsStateStateObject = { data: Record<PhetioID, LocalizedStringStateDelta> };
 
 const localeData = phet.chipper.localeData;
-assert && assert( localeData );
+assert && assert( localeData, 'localeData expected but global has not been set' );
 
 class LocalizedString {
 
diff --git a/js/getStringModule.ts b/js/getStringModule.ts
index 4b1808d70..fc4f9a73b 100644
--- a/js/getStringModule.ts
+++ b/js/getStringModule.ts
@@ -105,7 +105,7 @@ const getStringModule = ( requirejsNamespace: string ): object => {
   // Our locale information is from phet.chipper.locale
 
   assert && assert( typeof phet.chipper.locale === 'string', 'phet.chipper.locale should have been loaded by now' );
-  assert && assert( Object.keys( phet.chipper.localeData ).includes( phet.chipper.locale ), 'phet.chipper.locale should have been loaded by now' );
+  assert && assert( Object.keys( phet.chipper.localeData ).includes( phet.chipper.locale ), `phet.chipper.locale:${phet.chipper.locale} is not in localeData` );
   assert && assert( phet.chipper.strings, 'phet.chipper.strings should have been loaded by now' );
 
   // Construct locales in increasing specificity, e.g. [ 'en', 'zh', 'zh_CN' ], so we get fallbacks in order