I've been interested in learning about the Cossacks (in really any time period) and haven't been able to find much in the way of primary accounts from them themselves. I do not speak Russian/Ukrainian/Ruthenian, so even the things I have found have been unreadable for me. Can any experts point me in the right direction for this search? Anything in English would be helpful, however if there aren't many translations I understand as well.
There are works of literature that have been written by Cossacks, about Cossacks, which might be the best english-language option. Pyotr Krasnov, one-time Ataman of the Don Cossack Host during the Russian Civil War wrote from exile - https://en.wikipedia.org/wiki/Pyotr_Krasnov lists a number of his works, and there seem to be english versions. Mikhail Sholokhov wrote the very famous work "Quiet Flows the Don", which won him the 1965 Nobel Prize for literature, and it's less acclaimed follow-up "The Don Flows Home to the Sea". There are also some memoirs I located from people who lived with/near Cossacks and wrote about it: Francis McCullagh, With the Cossacks, being the story of an Irishman who rode with the Cossacks throughout the Russo-Japanese war. K.S. Karol's memoir Solik makes some mention of the Cossack culture surrounding him during and after WWII.
Also, you may already be familiar, but Shane O'Rorke has secondary sources called The Cossacks and Warriors and peasants: the Don Cossacks in late Imperial Russia. Serhii Plokhy also writes about Cossacks in english-languge secondary sources. Finally, I will add that Gogol's famous work Taras Bulba is about Cossacks - granted, not written by a Cossack. If I come across any memoirs, letter collections or the like written by Cossacks themselves, I will add them to the list.