I don't think removing a tax on retail gold purchases exactly means that a country has changed to a gold standard. A gold standard means there is gold backing the national currency. Arizona and other states do not charge sales tax on gold purchases.

Having visited Russia about 13-14 times, I can tell you that they have currency exchanges at every metro station and in each neighborhood, even in areas where there may not be a lot of tourists. My fees at Russian language schools were noted in EUR and I was asked to pay the equivalent at the time in RUB. There is a mindset of not trusting the ruble, and many people either kept USD or EUR bank accounts, or simply held foreign currency. Now that physical transport of USD and EUR to Russia may be difficult or impossible, removing sales tax simply makes it easier for the average person to keep wealth in gold, but by no means does this imply the existence of a gold standard.