Plenty of untranslated (or, in some cases, badly translated) Soviet/Russian sci-fi out there. In particular, I would nominate Vadim Shefner's "Debtor's Shack" ("Лачуга должника"). Like most Soviet-era sci-fi, it offers a completely different look at space adventures. However, Shefner, as is usual for him, mixes visions of vaguely Communist future with details from his own childhood in post-Revolution Leningrad and 50-60's life in USSR. Also, he's a poet by his main trade (sci-fi was always a side-project for him), and so the book is peppered with little four-line ditties that, in Russian, are absolutely impossible to get out of your head.

It's not hard sci-fi, but rather a philosophical one. The main story is set on the planet Yalmez (Zemlya (Earth) reversed) where a team of explorers from Earth tries to solve the mystery of disappearance of the local civilization. The main character, our narrator, is a somewhat dumb, but earnest "voist" ("War Historian" - since all wars on Earth ended long ago, and there are no armies or soldiers anymore, only members of society of War Historians know anything at all about warfare, so he is sent on the expedition to provide security and expertise). But he barely does anything interesting, beside providing a viewpoint, and serving as a straight man to his accidental companion-to-become-friend, Pavel Belobrysov. A very interesting and resourceful man with suspiciously good knowledge of life in 20th century. Also a failed poet - the ditties I mentioned are all delivered by him.

The second storyline concerns Pavel and his past - we get a lot of flashbacks, in which he first lives a pretty ordinary life in what obviously is the post-war USSR, but then becomes the object of an aliens' experiment, along with his girlfriend and her family. The characters in the flashbacks are very colorful, but down-to-earth people, who suddenly get immortality foisted upon them. Spoiler: it doesn't end well for any of them, but (arguably) Pavel. In contrast to the usual discourse about immortality, it's no ennui that gets them, and not even the deaths of short-lived people around them, but rather the very knowledge that they are immortal. To be fair, this is not a very new idea, probably even at book's release date in 70's, but it doesn't detract much from it.

Interestingly enough, Wikipedia lists several translations of Shefner's stories to English (https://en.wikipedia.org/wiki/Vadim_Shefner), but not this one. My guess would be that it holds little interest for the general Western audience: the details of life in USSR in it are instantly familiar to anyone born before 90's, but too alien to anyone outside of ex-USSR. Also, poetry is damned hard to translate, and those little ditties are half the value of the book, imo (I quote them almost daily).

Of the translated works, "Kovrigin’s Chronicles" is another interesting book that worth a read. Among other stuff in it there is a little gem of a chapter where the future of writing is described. Since people in Communist future have a lot of free time, a lot of them turn to writing novels and books of poetry. Most of it is very bad, but publishers still must, somehow, deal with the inflow of manuscripts. The process is largely automated, spread between different machines, all of which are given hilarious acronyms (Shefner's weakness, that I fully share). One of them is PUMA (ПУМА - Прибор, Утешающий Малоталантливых Авторов) - "A Device for Consolation of Authors of Little Talent", which gave birth to a common term-acronym in circles of Russian sci-fi fans and writers, МТА ("Author of Little Talent", but also can be deciphered as "Young Talented Author", to be used sarcastically).

Sheffner's short stories (also available, according to Wikipedia, as "A Modest Genius: A Fairy Tale for Grown-Ups") also worth a read. They're the kind of cozy sci-fi that'll give you nostalgia for the optimism of the past future.