"O pâine, nu două pâini."
Translation:A loaf of bread, not two loaves of bread.
The translation doesn't sound quite right as bread is usually an uncountable noun. But bread can be used as a countable noun if, for example, referring to different types of bread. I suggest a more common translation would be 'A loaf of bread, not two loaves of bread'
Perhaps I'm totally missing the point here - it looks like bread is a countable noun in Romanian.
You're not missing the point, you're absolutely right. To clarify, "pâine" can be both countable and uncountable in Romanian. When used as a countable noun, it means exactly "a loaf of bread".