Vietnamese were chosen as applicable law, should the CISG govern contract ? May the parties choose laws of Indonesia to be applicable of the contract?

Question

The contract is signed between the company, which is located in Vietnam, and company in France / Germany / Australia / Korea.
From the Contracting States of CISG between Vietnam and U.S. activated, the National laws shall be replaced with the CISG applied as governing law.
I want to ask you:

Vietnamese were chosen as applicable law, should CISG govern contract ? May the parties choose laws of Indonesia (not Contracting States of CISG) to be applicable law of contract?

I need your help. Thanks a real lot !

Answer 1

If a contract was formed, that contract is governed by the law named in the contract, in this case, the law of Vietnam rather than the CISG, so long as the contract provision doesn't violate public policies making it void in the legal forum in which the contract is enforced.

For example, if the law of Vietnam allowed for 100% per year interest but the law of Australia did not, a court in Australia might refuse to enforce that interest rate, even though the contract provides that the law of Vietnam applied to the contract.

Arguably, the CISG governs whether a contract was formed in the first place, since, without formation of a contract, there is no choice of law provision to enforce.

However, in the case of a written agreement signed by all parties to the agreement, the CISG and the law of Vietnam and the domestic law of every other country mentioned in the question would be unambiguously find that a contract was formed, so the choice of law is irrelevant as to that legal issue.