For cheese in general: If a cheese is not a processed cheese (manufactured) but is a cheese that has had a bacterial culture involved with its production and is aged at least 30 days. Elaine says its OK.
Further to the above I have read that Bulgarian cheese may be similar to feta cheese. Here is what Elaine wrote about Feta: Feta
In response to a question about different types of Greek cheeses, Elaine writes:
Just went to your great cheese website and looked up Kaseri. It says, "Kaseri is used in Greece instead of mozzarella and appears in local dishes." By all indications, Kaseri is not a cultured cheese (treated with a bacterial culture and aged) and if it is really is like mozzarella, it is illegal. The fact that it is very salty suggests that it is preserved by salt and not by culturing. One of the questionable cheeses that it sounds like is Feta. I have placed Feta and Mozzarella in the illegal cheese columns. However, Feta may be used after about 6 months of improvement. But used only in small amounts.
So, if it has a bacteria culture and is aged at least 30 days it is good. Or if it is more like traditional feta then after 6 months improvement