Categories are in single-language hierarchies. Dominican Republic is the correct category title within the English language hierarchy. As an aside, most often we just use the brief formal name without the longer title, i.e, we say France, not Republic of France. But we say "United Kingdom" because the name would be meaningless without it, and the same applies to both Dominican Republic and Republica Dominicana.
It would make sense to create categories in Spanish for the Dominican Republic. They simply need to be consistently in Spanish. They can be cross-referenced to the parallel English language category. I think if I were in your shoes, I'd create the location categories that you need using the Spanish names, and not bother creating any English language parallels that have not already been created, unless a special need should appear.
Does the Dominican Republic fall within a current project? If there is, you should coordinate with the project and also the Categorziation project. If not, you will find it helpful to collaborate with others who have done category hierarchies in non-English languages.