past perfect,past tense or present perfect?

[njanja]

Imagine how good your English would be,if you had lived in an English - speaking country for ten years.
.................................................. ....,if you lived...
.................................................. ....,if you have lived...

Thanks.

[Tdol]

Imagine how good your English would be,if you had lived in an English - speaking country for ten years.
This is fine; it is talking about the past and the fact that you didn't live in such a country for ten years- maybe you were only there for one, or didn't go at all.

Imagine how good your English would be,if you lived in an English - speaking country for ten years.
This is also fine; it's talking about an imaginary situation- you are not going to live in an English-speaking country for ten years.

[dihen]

for ten years- maybe you were only there for one, or didn't go at all.

I would want to say "for one year", not just "one" because for me, it means "for someone".