Using たら, how do I say "would have" instead of "would"


I'm struggling to understand how I can change the tense of conditional
sentences.

For example, if I want to say "If I were him, I wouldn't say such things" I
presume I would say "もし私が彼だったらあんなことは言わない". But if I want to say "If I were
him, I wouldn't have said such things" should I say "もし私が彼だったらあんなことは言わなかった" ?




「あんなことは言{い}わなかった」 would be quite acceptable in non-formal speech. It would
easily be understood to mean "I would not have said ~~" by native speakers
_**if used in the right context**_.

You should, however, be at least aware that _**grammatically speaking**_ ,
「言わなかった」 is only in the simple past tense.

More formally and/or academically, you can say:

> 「言わなかった **であろう** 」 and its shorter version is:
>
> 「言わなかった **だろう** 」

It is also very natural and common to say:

> 「言わなかったと思{おも}う/思います」

