I can't believe this keeps popping up in such a highly monocled environment as the Codex undoubtedly is.
Bonus is pig-Latin, proper Latin would be using the substantivized adjective in its neutral form (bonum, plural bona).
Bonus as a substantivized adjective means 'good person/good man', not 'good thing' (that would be bonum).
So bonus in the way it's used should be treated as an English word.
Some languages might have adopted the usage of a plural Latin form for words that are derived from Latin. That doesn't necessarily mean that these words themselves are the same original Latin words just that a language allows an alternative form of plural because of their origin. I believe at least some Germanic languages allow usage of "boni" as the plural to "bonus". Both "die bonusse" and "die boni" are acceptable forms in German AFAIK, I might be wrong about that. I'd need a German native speaker to confirm but that's what the German Wiktionary claims.
In English on the other hand, it doesn't seem to be the case, certainly not for the word "bonus" anyway. It's just an English word with plural "bonuses".
I'm saying all this because that might be the source of confusion here. We have tons of foreigner posters (myself included) and they might sometimes tend to copy the rules of their native languages into English.