fix(frontend): prevent LanguagePicker crash when locale is missing from LANGUAGES config (#39585)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

superset-frontend/src/features/home/LanguagePicker.tsx

@@ -25,9 +25,9 @@ import { Typography } from '@superset-ui/core/components/Typography';
 
 export interface Languages {
   [key: string]: {
-    flag: string;
-    url: string;
-    name: string;
+    flag?: string;
+    url?: string;
+    name?: string;
   };
 }
 
@@ -61,9 +61,9 @@ export const useLanguageMenuItems = ({
       key: langKey,
       label: (
         <StyledLabel className="f16">
-          <i className={`flag ${languages[langKey].flag}`} />
-          <Typography.Link href={languages[langKey].url}>
-            {languages[langKey].name}
+          <i className={`flag ${languages[langKey]?.flag ?? 'us'}`} />
+          <Typography.Link href={languages[langKey]?.url}>
+            {languages[langKey]?.name}
           </Typography.Link>
         </StyledLabel>
       ),
@@ -75,7 +75,7 @@ export const useLanguageMenuItems = ({
       type: 'submenu' as const,
       label: (
         <span className="f16" aria-label={t('Languages')}>
-          <i className={`flag ${languages[locale].flag}`} />
+          <i className={`flag ${languages[locale]?.flag ?? 'us'}`} />
         </span>
       ),
       icon: <Icons.CaretDownOutlined iconSize="xs" />,