Are somebody sure that "deseara" is equal to "tonight"? In bulgarian we have more suitable word which means " in the evening" - довечера and it comes from the вечер - evening.
Seară=evening, deseară = this evening. Evening and night are interchangeable in many contexts, as there is no exact time that separates these both. Evening is ”beginning” of night.
Along the line of "regionalisms"... here (New England), we often say, "I'm making dinner" but "I'm cooking dinner" is also used.