Here’s a list of speculative fiction (novels and novellas) by Arkady and Boris Strugatsky, both translated into English and not yet translated:
From Beyond
novella
translated by ?
Soviet Literature 1, 1982, pp. 8-36
The Land of Crimson Clouds (1959)
novel (set in the Noon Universe)
not translated
The Way to Amalthea (Destination: Amaltheia) (1959)
novel
translated by ?
Foreign Languages Publishing House, Moscow, 1963
Noon: 22nd Century (1961)
novel/collection of linked stories (set in the Noon Universe)
translated by Patrick L. McGuire
Macmillan, 1978
Space Apprentice (Probationers) (1962)
novel (set in the Noon Universe)
translated by Antonina L. Bouis
Macmillan, 1981
Escape Attempt (1962) (includes Space Mowgli (1971) and The Kid From Hell (1974))
novella (set in the Noon Universe)
translated by Roger DeGaris
Macmillan, 1982
Far Rainbow (1963)
novel (set in the Noon Universe)
translated by Antonina W. Bouis
Macmillan, 1979
Hard to be God (1964)
novel (set in the Noon Universe)
translated by Wendayne Ackerman (Seabury Press, 1973)
translated by Olena Bormashenko (Chicago Review Press, 2014)
Monday Starts on Saturday (1965)
novel
translated by ? (DAW Books, 1977)
translated by Andrew Bromfield (Chicago Review Press, 2017)
The Final Circle of Paradise (1965)
novel
translated by ? (DAW, 1976)
The Snail on the Slope (1966-68)
novel
translated by Alan Meyers (Gollancz, 1980)
translated by Olena Bormashenko (Chicago Review Press, 2018)
The Ugly Swans (written 1966-67; first published 1972)
novel
translated by Alice Stone Nakhimovsky and Alexander Nakhimovsky (Macmillan, 1979)
The Second Invasion From Mars (1968)
novella
translated by Antonina W. Bouis (Macmillan, 1979)
Tale of the Troika (1968)
novella
translated by Helen Saltz Jacobson (Macmillan, 1977)
Prisoners of Power (1969)
novel
translated by Helen Saltz Jacobson (Macmillan, 1977)
The Inhabited Island [new translation of uncensored version of Prisoners of Power]
novel
translated by Andrew Bromfield (Chicago Review Press, 2020)
The Dead Mountaineer’s Inn (1970)
novel
translated by Josh Billings (Melville House, 2015)
Roadside Picnic (1972)
novel
translated by Antonina W. Bouis (Macmillan, 1977)
translated by Olena Bormashenko (Chicago Review Press, 2012)
Definitely Maybe (1977)
novel
translated by? (Macmillan, 1978)
translated by Antonina W. Bouis (Melville House, 2014)
The Doomed City (written 1975, published 1989)
novel
translated by Andrew Bromfield (Chicago Review Press, 2016)
Beetle in the Anthill (1979)
novel (set in the Noon Universe)
translated by Antonina W. Bouis (Macmillan, 1980)
The Time Wanderers (1985)
novel (set in the Noon Universe)
translated by Antonina W. Bouis (Richardson and Steirman, 1987)