Adds 'Vietnamese' to the list of available languages in the cross-language item components (#8843)

### What problem does this PR solve?
This change adds 'Vietnamese' to the list of supported languages in two
components related to cross-language functionality. The addition expands
language support by including Vietnamese as a selectable option

### Type of change
- [x] New Feature (non-breaking change which adds functionality)

web/src/components/cross-language-item-ui.tsx

@@ -10,6 +10,7 @@ const Languages = [
   'German',
   'Japanese',
   'Korean',
+  'Vietnamese',
 ];
 
 const options = Languages.map((x) => ({ label: x, value: x }));

web/src/components/cross-language-item.tsx

@@ -9,6 +9,7 @@ const Languages = [
   'German',
   'Japanese',
   'Korean',
+  'Vietnamese',
 ];
 
 const options = Languages.map((x) => ({ label: x, value: x }));