[germanier]

> I don't know any loanwords that break english pluralization rules in german

The plural of 'Baby' is 'Babys' (instead of 'Babies' – though some people also use that form) and 'Computer' doesn't change.

On the other hand, both 'Indices' and 'Indexe' are used and for 'Tempus' the only plural is 'Tempora'.