"Quiero comprar dos pares de zapatos."
Translation:I want to buy two pairs of shoes.
Actually, only "pairs" in correct. Two shoes (left and right) equal one pair of shoes. Four shoes (2 left and 2 right) equal two PAIRS of shoes. The Oxford's Learners Dictionary says this: In informal North American English some people use pair as a plural form: three pair of shoes. This is not considered correct in written English.
According to Google Ngram Viewer , Google Ngram Viewer and Google Ngram Viewer , "pair" as a plural was more popular than "pairs" in the late 18th century and has been losing popularity since then. I heard it all the time when I was a kid in rural Michigan in the 1970s, but I haven't heard it as much lately.