The provisions of this chapter relating to the transfer of offenders shall be applicable only when a treaty providing for such a transfer is in force, and shall only be applicable to transfers of offenders to and from a foreign country pursuant to such a treaty. A sentence imposed by a foreign country upon an offender who is subsequently transferred to the United States pursuant to a treaty shall be subject to being fully executed in the United States even though the treaty under which the offender was transferred is no longer in force.