The countries that don't allow dual citizenship for adults as of this writing include:
Bahamas.
China.
Haiti.
Indonesia (except in certain circumstances)
Japan.
Kuwait.
Laos.
Malawi.
People Also Ask
Generally, Spain does not permit dual citizenship with another country other than with Iberian countries. If you obtain Spanish citizenship, you will have to renounce your original nationality. There are exceptions, including Spanish-American countries, Andorra, the Philippines, Equatorial Guinea or Portugal.