Una volta controllato il contratto, prepariamo la controproposta.

Here una volta does not mean one time in the literal counting sense. In this sentence, una volta + past participle is an idiomatic way to mean once, after, or when ... has been done.

So:

Una volta controllato il contratto
= Once the contract has been checked / After checking the contract

It introduces an action that must be completed before the next one happens.

Controllato agrees with il contratto, which is masculine singular.

That is why you get:

• controllato il contratto = masculine singular
• controllata la fattura = feminine singular
• controllati i documenti = masculine plural
• controllate le clausole = feminine plural

So the participle matches the thing that has been checked.

Because Italian often uses a shortened participial structure after expressions like una volta.

The full idea could be expressed in other ways, such as:

• Una volta che abbiamo controllato il contratto, prepariamo la controproposta.
• Dopo aver controllato il contratto, prepariamo la controproposta.

But una volta controllato il contratto is more compact and very natural in formal or business-style Italian.

Usually the sentence suggests that the same people who prepare the counterproposal are also the ones who check the contract, so in context it is naturally understood as we.

However, this structure is slightly less explicit than saying:

Una volta che abbiamo controllato il contratto...

So it can sound a bit more neutral, almost like:

Once the contract has been checked...

In many real contexts, the reader understands from context who is responsible.

Italian often uses the present tense where English might use either the present or the future, depending on context.

Here prepariamo can mean things like:

• we prepare
• we then prepare
• we will prepare

It can sound like:

• a routine procedure,
• a plan,
• or a step in a process.

So the present tense here is very normal.

This is a very common question because it looks like an English cognate.

In Italian, controllare very often means:

• to check
• to inspect
• to review
• to verify

It can sometimes mean to control, but in many everyday and business contexts, to check is the better translation.

So in this sentence, controllare il contratto means to check/review the contract, not to control the contract.

Controproposta means counterproposal or counteroffer, depending on context.

In a negotiation, it is the proposal you make in response to someone else's proposal.

So:

• proposta = proposal
• controproposta = counterproposal

In a contract or business setting, both counterproposal and counteroffer may work in English, depending on the exact situation.

Italian uses definite articles more often than English does.

Here il contratto and la controproposta suggest specific items that are already known in the situation:

• the contract
• the counterproposal

Even where English might sometimes omit an article or sound less definite, Italian often keeps it.

So this is completely normal business Italian.

The comma is very natural here because Una volta controllato il contratto is an introductory clause placed before the main clause.

So the sentence is divided into:

• introductory time clause: Una volta controllato il contratto
• main clause: prepariamo la controproposta

In writing, the comma helps readability and is standard here.

Yes, absolutely.

Dopo aver controllato il contratto, prepariamo la controproposta is a very natural alternative.

The difference is mainly stylistic:

• Una volta controllato il contratto = more compact, slightly more formal, focused on completion
• Dopo aver controllato il contratto = more explicit, very clear, also common

Both are correct and natural.