a) Well, the language problems didn't influence the result of the talks. (can't)
The language problems {input: can't have influenced} the result of the talks.
b) Perhaps the name of the product was the problem. (could)
The name of the product {input: could be} the problem.
c) You wasted your time going there. (oughtn't to)
You {input: oughtn't to have gone} there.
d) Adapting the product was a bad decision. (shouldn't)
The product {input: shouldn't have been adapted}.
e) It is better to keep our main objective. (ought)
We {input: ought to keep} our main objective.
f) May be they're having trouble working together. (might)
They {input: might have} trouble working together.
g) I suppose the team misunderstood the brief. (may)
The team {input: may have misunderstood} the brief.
h) I apologise for interrupting, but is it possible to make a suggestion? (could)
I apologise for interrupting, but {input: could I make} a suggestion?