There are two main answers: Turkmen and of course, Russian, and it can be hard to know when to use each one. As a general rule everyone does speak Russian, but most people do appreciate the effort if you're able to throw in some Turkmen, even just as a gesture.

Does Tajikistan speak Russian?

A generation ago, Russian was the primary language of Tajikistan's cities, but today it is spoken mainly by a dwindling elite. Due to war and economic decay over the past two decades, hundreds of thousands of the best-educated Tajiks – generally Russian-speakers – have left the country.

Is Turkmen part of Russia?

1925 - Turkmenistan becomes a fully-fledged constituent republic of the USSR. It does not gain independence until 1991. 2009 December - Pipeline opened for gas exports to China, breaking Russia's stranglehold on Turkmenistan's energy reserves.