If I make someone from another country sign an NDA would that be valid without reasonable doubt?
A contract is only as good as the ability to enforce it. It depends on what the other country is and how well their court system works. In any case, if someone violates an NDA, taking them to court over it is likely to be expensive, so I would use an NDA more as a threat and an insurance policy and not count on actually being able to enforce it.
Talk to an international attorney. If the party signing it is in your country, then it is obviously more enforceable. If the NDA is with a partner in another country, and the jurisdiction of dispute is in your country, you have to get that individual to travel to your country to go to court. Which...think about it..why would they if they stole your IP? The other issue is where thier are assets are...if they have no assets in your country, and for whatever reason they chose to come to court to dispute and you won...you would still have to gain access to their assets..which if they are in another country...that will be a challenge. Beware of companies in China and India, as the international lawyers I know have warned they have the highest rate of the above problems. In other words if you are partnered with someone in China...they steal your IP....and you try to bring them to court in London..they will likely say "Good luck with that buddy..have a nice day." Obviously depending on who your lawyers are...that impacts the enforceability.
Your focus should likely be on your territory. Once you scale out to other countries, if you are global you are likely going to be spending several million in IP enforcement. But hopefully at that point your revenue will be in the hundreds of millions and it wont hurt your bottom line..at least not anywhere near as much if the violations are allowed.
All RN co-founders had to sign NDA agreements. We are very international team, but still need to sign contracts, including NDAs.
NDA reminds of what parties can do/share and what is not allowed. So this doc is needed
Another issue to consider is who and why you are presenting an NDA. Prospective investor, employee? If it is an employee, there are other agreements that can be tied into the NDA that will better protect you. As for the advice not counting on being able to enforce it....eghh...not really the proper way to approach any contract. I come from the mentality of utilize contracts to the best of your ability with the 100% intent that if they are broken in a way that hurts you or your company in a manner substantial, that you prosecute those who violated.
Moving your business forward with an intent to not uphold contracts or laws that have precedence...or bluff will likely come through in your tone and approach. If you can't afford to sue if a violation occurs that is one thing. But approach it as if you have a top tier lawyer on retainer for your company (which you very may well down the line at the time the NDA is violated) and position yourself to command respect and adherence to the law and to the contracts you put in place. Any contract is only as powerful as the attorney behind it, and if someone violates your NDA, a smart attorney will find the way to justify the situation.