if I moved bitcoin outside of the US and to an El Salvador wallet, would that be saving on the future sale of bitcoin or what would that look like for capital gains?
You need to understand that your coins are not in your wallet but rather on the block chain, your coin only bears the keys which is needed to access it on through the wallet to decrypt the encrypted access through your private keys.
secondly, you don't need to change location before you can have your coins in safety, as long as you're using a decentralized exchange wallet.