Add additional localization strings for itinerary features in Polish, Swedish, and Chinese

- Added "additional_info", "invalid_date_range", "sunrise_sunset", and "timezone" keys to pl.json, sv.json, and zh.json.
- Updated existing strings for consistency across languages.

frontend/src/locales/en.json

@@ -63,6 +63,7 @@
 		"collection_remove_error": "Error removing adventure from collection",
 		"collection_link_success": "Adventure linked to collection successfully!",
 		"invalid_date_range": "Invalid date range",
+		"timezone": "Timezone",
 		"no_image_found": "No image found",
 		"collection_link_error": "Error linking adventure to collection",
 		"adventure_delete_confirm": "Are you sure you want to delete this adventure? This action cannot be undone.",