we could hear if anyone came along the trail.

I think it's OK except for the last clause, which should be either "...so quite we would hear if anyone came along the trail" or "...so quiet we could/would hear anyone come along the trail"

But you should know I am not fluent in English, if to put it midly...

Thank you, Ant. I actually debated whether to include 'if'. I feel that without 'if' as in your latter suggestion, it's still conditional. What do you think?

Regarding could or would, I feel both are OK. In other words, all your suggestions sound good to me. And I don't see anything wrong with the original, of course, otherwise, I would not have written it

"I feel that without 'if' as in your latter suggestion, it's still conditional. What do you think?"

Conditional with "would", but not with "could". Also note that the omission of "if" is not the only change I made: I also replaced "came" with "come". That's essential.

"And I don't see anything wrong with the original, of course, otherwise, I would not have written it

New2grammarI don't see 'if' as a reason not to use 'could'.

Your reasoning is correct. could here means would be able to, so would is implicitly included already within could.
CJ

Ant_222 I also replaced "came" with "come". That's essential.

I noticed that. I would have done that too as hear is followed by a bare infinitive. However, the past tense is probably possible if 'that' is implied.For example, I heard (that) he talked to you.

"I heard (that) he talked to you."

It's correct, but the meaning is totally different.

"I heard he talked to you" — "Someone told me he that he had talked to you".
"I heard him talk to you" — You were the direct witness, you heard the talk.

Ant_222"I heard he talked to you" — Someone told me he that he had talked to you.
"I heard him talk to you" — You were the direct witness, you heard the talk.

Yes. Exactly. But it doesn't make the original wrong, does it?

Yes — CJ confirmed you, although I still don't quite understand how 'could' works...

Ant_222Yes — CJ confirmed you, although I still don't quite understand how 'could' works...

Sorry, I got myself confused. I was referring to
we could/would hear anyone come along the trail"

Can I say 'came'?

(EDIT: I don't think "CJ confirmed you " is correct. It shoud be CJ confirmed your 'something' or he agreed with you)

Although you are right about "confirmed", I think it's incorrect to say "We could/would hear anyone came along the track".