Final answer:
The best option is to secure a specialized third-party vendor to provide a customized settling-in program for the international assignee.
Step-by-step explanation:
The best option to help an international assignee rapidly acclimate to the new country's culture is to secure a specialized third-party vendor to provide the assignee with a customized settling-in program. This option ensures that the assignee receives personalized support and guidance in adjusting to the new culture. The customized settling-in program can include various aspects such as language and customs courses, cultural orientation, and assistance with housing, education, and other essential needs. This comprehensive approach helps the assignee navigate the challenges of the new environment and facilitates their integration into the local culture.