If my wife leaves me and gains costody of our kids, can she move to another COUNTRY?

Depends on what type of custody she gets. If you're getting divorced try to get joint custody, that means you have to agree to it. If she gets sole custody, you have no say.

It will depend as stated on the terms of the divorce.

But I will note, if she is from another country, even if she loses custody and on a time of her visitation, just leaves the county with them to another country, ( depends on the country) it is often very hard if even possible to get them back.

If she has sole custody and the court order doesn't specifically prohibit it, then yes. If you are concerned about this happening then you need to ask the judge to address this when you go to court for custody. Aim to get joint custody and a stipulation that she may not move the children out of the country.