As it turns out, the second paragraph [of the Ley de Alquileres] --the paragraph that talks about payment being only in the moneda de curso legal --was
stricken down by the Ministry of Economy in 1993 after reviewing a law passed in 1991.
Original law here.
According to
Resolution 144/93, which specifically mentions rentals, landlords can use any currency they wish to use. The most important part: "Artículo 1º — Interprétase que la Ley 23.928 ha derogado el segundo párrafo del artículo 1º de la Ley 23.091, pudiendo las partes contratantes determinar la moneda de pago de los alquileres o arrendamientos que acuerden." (In other words, the second paragraph of the original law no longer applies, and now the parties signing the contract may use whichever currency of payment that they choose.)