Diplomatic Personnel Modernization Act This bill requires the Department of State to submit to Congress a comprehensive five-year strategic staffing plan. This plan must include (1) a data set displaying comprehensive workforce data for all current and planned State Department employees, disaggregated by certain metrics; (2) recommendations on the number of Foreign Service officers that should be posted at each U.S. diplomatic post and in the District of Columbia; and (3) recommendations on the number of civil service officers that the State Department should employ.