The official language in Romania is Romanian.
Romanian is a Romanic language, the Italic group of Indo-European family of languages. It has many similarities with French, Italian, Spanish, Portuguese, Catalan and Rhaeto-Romance languages.
Although in almost all research institutes you can communicate in English, it is still appropriate to take Romanian language courses, as your stay in Romania is not just about work, and knowing the language will help you integrate more easily.
Foreigners can learn Romanian both in private institutions and in various universities that offer support to all interested persons. Such centers exist in almost all cities in the country.
Courses are offered at 3 levels: beginner, intermediate and advanced.
Please note that in Romania in every major city there are French, German, Italian, Spanish (and so on) cultural institutes and centres. Some of them offer even Romanian classes for foreigners, depending on their course policy.
Below you will find some useful links towards language centres that offer Romanian courses.