“Nego” and “već” are especially frequent and often do not need to be rendered as “but” or “already.” In fact they often don’t need to be translated at all, or rather their translation is a non-word in English, a sort of translation by omission or translation by silence. An example of the latter:
Samo željeznica nije trunula i urušavala se, nego je postojala onakva kakva je bila i u prethodnih stotinu godina, s redom vožnje kao svojim jedinim katekizmom.
The nego here draws contrast and one could of course render it as “Only the railroad/railway had not collapsed and destroyed itself but existed exactly as it had for the preceding hundred years….” But when this or similar nego constructions are frequent (and they are, as in the correlative construction “not only… but also,” then some variation and economizing can help move the prose along: “The railway was the only thing that had not collapsed and destroyed itself, remaining exactly as it had been for the preceding hundred years, with the timetable as its sole article of faith.”
For the last word in the sentence, katekizam, whose English equivalent would in other contexts be “catechism,” the emphasis on one (jedini) thing suggests that “article of faith” is a better solution, especially since the sentence before this suggests that the RR had outlived both Hitler and the two-thousand-year-old faith in Jesus Christ.