I'm writing a story with a Russian soldier, and I usually put her swearing into Russian so as to not be immediately offensive to English readers.
So, the word that I'm needing is "fuckers". To put it in context, the line is: "How does it feel to burn—just like all the people on all the planets you [fuckers] glassed?"
What's the right word that I would need for this?
"Твари" or "мрази" are the best words I can think of. Neither of them are truly obscene, though. The genitalia-derived obscenities offered in other answers have something comical about them, not something you would seriously call a strong and dangerous enemy who has glassed so many planets (unless you want to portray the situation with a degree of humor). When you call a person something like "уёбок" or "долбоёб", the nuance is that he is a somewhat inept person, doing his bad things at least partially out of stupidity.
Can't refrain from offering my very valuable opinion on the matter in general. I am a native speaker of Russian with semi-decent English. I also speak enough Japanese to get by. I like cursing (yes, in all three languages) and often do, but can't remember ever using a curse from a language foreign to the one I am speaking at the moment. That would just feel sooo awkward. The grammar is different, the phrase composition is usually different enough so that there's simply no good place to insert a foreign curse into. The way you [are trying to] pronounce "corresponding" sounds in different languages is also different, should I pronounce it like I would in English, e. g. "moo duck", or the plain Russian "мудак" will do? Switching takes enough time and mental effort to kick you out of the flow. The closest thing to your example I can imaging myself saying is something like: "What are you doing, you... you... [struggling to remember the word "faggot" for a second and failing]... пидор!"
And no, "Clockwork Orange" is not a good counter-example, what's described there is a sub-cultural phenomenon of taking a very limited subset of foreign words and adapting them to English grammar and phonetics.
It's уёбок or ушлёпок.
I'd go with уёбки (singular уёбок) or уебаны (singular уебан) - this is exactly something like fuckers.
It's comparably more neutral than ебанат, there's also word долбоёб but it's more like stupid fucker.
There's also мудила but it's more like stupid asshole or douchebag.
So, "уёбок", definitely "уёбок" :)
Or if want to use something similar but less abusive (because the root ебать from which уёбок is derived is highly offensive and not acceptable in the majority of cases, it's not like fuck in that sense) - use ушлёпок - this is exactly the same but you can use it, say, on TV without the risk of being ostracized.
уёбище (щ, not ц) is yet another form of уёбок
The people above try to get a rough translation, while in this situation I would look for an equivalent, not exact translation
I would go with one of the following
somewhat mild variations
obscene variants
Please, note: obscenities in russian are considered to be obscenities: they are 'beep'ed on tv and are not allowed in civil settings. Refined people never use them, and even unrefined people do not use them in formal settings. Very few people would use obscenities in formal settings, and this is not considered acceptable. A truly refined person should be able to make opponent cry from understanding of own low place in life without obscenities.
I think "суки" would go good in this situation. It is plural of "сука" which means "female dog" but also has a meaning "bitch" and can be applied not only to female persons.
Just take explicit-language-aware translations of Hollywood war movies and look at situations what would suit you.
Two lists of movies and download link.
The first link gives you list of movies you might want to look into. The second - the list of movies you definitely need to stay away from, in the context of this work. The third - should let you download subtitles to the movies you selected and read them.
Then, still you would have to make her language consistent with her cultural background, with her past. Because expletives can be translated rather vague, and if you would pick different style, different semantic cloud expletives - it would sound chaotic and weird for her personality.
When Barry Longyear was writing a novel about blinded woman, he not only lived few weeks with eyes covered, he also allegedly wrote a full bio of that woman, that was scrapped later, but that provided all the details and nuances he needed in the published novel.
Considering the context of your presumably fantastic novel, where the character is addressing an alien life form, I guess the best option would be пидорасы (lit. homos, or faggots).
But since you are writing about a female character, I think a recently developed feministic swearing хуемрази (ед. ч. "хуемразь", literally smth like 'dick-bastards' or 'dick-creatures') would do.
But, again, we don't know much about the races and sexes (if any) of her addressees--
