We have been waiting long for this to be completed.

[tufguy]

How long will you take to complete this work? We cannot wait any longer. We have been waiting long for this to be completed.

Do we say "We have been waiting/waited long for something" or do we say "We have been waiting/waited for long for something"?

 

[bhaisahab]

'We have been waiting too long...' or 'We have been waiting a long time...'

 

[Charlie Bernstein]

I like a long time.

If it's a really, really, really long time, we often say we've been waiting forever.

 

[emsr2d2]

"Long" on its own works in the interrogative and in the negative, but not in the positive.

Have you been waiting long? :tick:
I haven't been waiting long. :tick:
I have been waiting long. :cross:

 

[tufguy]

"Long" on its own works in the interrogative and in the negative, but not in the positive.

Have you been waiting long? :tick:
I haven't been waiting long. :tick:
I have been waiting long. :cross:

We have been waiting a long time or we have already waited for a long time. Are these correct?

 

[emsr2d2]

​1. We have been waiting a long time. [STRIKE]or[/STRIKE]
2. We have already waited for a long time.

Are these correct?

We told you, not too long ago, to ask us about one sentence at a time. You seem to have forgotten that already. I have amended your post above, just this once, so that it's easier for us to reply.

Both sentences 1 and 2 are grammatically correct. Which one you choose would depend on the context and the situation.