There's a book in Russian, German Noskin, First computers for space applications (Герман Носкин, Первые БЦВМ космического применения), ISBN 978-5-91918-093-7.
The author himself participated in many early projects (mostly in hardware) and according to him analog hardware was in favor for a long time, he mentions that space rendezvous tasks didn't use digital computers until late 70-s. Due to this policy many digital computers were really proofs of concept although used in other areas of soviet economics. The first computer according to him used on-board was Argon-11S (Аргон-11С) on the unmanned missions to the Moon closer to Appolo-8 in time. Also Noskin briefly says that on-board computer Salut-4 was compatible with general-purpose computers ES used in soviet economics so it was possible to develop software in PL-1 and Fortran.
There are several mentioning of Buran program languages at russian web. According to Vladimir Parondjanov, an engineer from the program (russian post) three languages using Russian as a base were developed: PROL2 (ПРОЛ2) for onboard programs, Dipol (Диполь) for earth tests , Laks (Лакс) for modelling. All of them were intended for usage not only by professional programmers but also engineers from other areas.
When Buran program was closed they were merged into a new language Drakon (Дракон, Russian word for "Dragon") that is claimed to be be a "graphical" language having 2-dimensional descriptions of the programs and using arbitrary well-known languages for code generation. This language is also intended for using by non-programmers. The language is probably has no international community and also not well-known in Russia although heavily promoted by his author, Vladimir Parondjanov (the Russian Wikipedia article article is very long and was even deleted once for not following Wikipedia rules). Drakon was firstly used for programming Sea Launch missions and were used in other russian space programs ever since