I have some bitcoins that I've kept for a couple of years and I'd like to sell them for a profit, without paying a big tax on it, and then to transfer the money through bank transfer to my country. Here in my country I'd have to pay 20%, which is not acceptable.
If you are a United States taxpayer, you can’t. You can stash your funds in bitcoin, hold them, but when you convert into fiat, there will be a trace. All exchangers have the obligation to report to the IRS (AML/KYC and BSA compliances). If you have a friends in these crypto friendly countries then maybe they can help you to evade taxes but I think the chances are small.