Translation:The deceitful comrade does not fight.
Perfidus needs many more acceptable English translations, including faithless.
Agreed. Same with "comrade". It's hard to imagine an English speaker producing the phrase, "The deceitful comrade..." in normal speech. (Maybe as the title of a Sherlock Holmes fan-fic?")
Maybe "treacherous ally" or "fair-weather friend" or something?
I put "faithless friend." I think a variety of translations are in order.