No. Used to be, not so important anymore.
Today’s fiat currencies are not backed by gold reserves. In fact, the only thing they are backed up with is a promise. The full faith and credit of the government. Nothing more and nothing less.
Countries today invest in gold reserves because they fear at some point in time, a country’s wealth may again indeed be looked at by the amount of gold reserves they have, and thus they continue to invest in gold reserves, but such wealth is not linked to their ability to print more (or less) paper money.
Investopedia has a really great article on the gold standard: What is the gold standard?