As far as I know, it’s always valid, and perhaps even preferable, to use the regular -s plural with any Latin loanword, after all they’re English words now even

As far as I know, it’s always valid, and perhaps even preferable, to use the regular -s plural with any Latin loanword, after all they’re English words now even if borrowed from another language. Using the original Latin plural forms in casual contexts feels a bit pretentious, especially when it’s not even the correct form, like "octopi".