bulgarian language exam for citizenship?

From what I understand, citizenship can be applied for after 10 years of residence... 5 years of prolonged residence (where you renew it every year) and then another 5 years of permanent residence (where you renew it every 5 years) and THEN citizenship. I believe there is an interview conducted in Bulgarian language for citizenship, but I am not sure if there is a written exam.

Residence is after 5years for members of the EU, are the regulations different for those outside of the EU?

Yes, the rules are different for those outside of the EU.

Non-eu citizens have to apply for a temporary residence permit for 5 years before they can apply for the 5 year extended residence permit. (That means that every 6 months or every 1 year, the individual has to pay a tax and apply for a permit again--- after continuing to do this for five years, without interruption, they can apply for a permit that is good for another five years.)

EU residents and their spouses (but not Bulgarian spouses) can skip the first five years of temporary residence permits and immediately get the five year permit when they arrive. Applying for citizenship requires that you have had the five year extended residence permit for five years... meaning non eu citizens need 10 years in Bulgaria (7, if they have a Bulgarian child, because they can get the 5 year permit after only 3 years of temporary permit) whereas eu can apply for citizenship after just 5 years.

The quickest way to citizenship for a non-eu citizen is to actually marry an eu citizen other than a Bulgarian, as then they could immediately get a five-year permit and apply for citizenship after five years.

I think there may be different rules if you invest a large sum of money in Bulgaria.

Also, you need to pass a language exam. Bulgarian is distantly related to Persian but I think it is difficult. But not as difficult as Russian