In Mr. Medellin's case, the Mexican government is playing the part of a juvenile's parents - but in no way is the jurisdiction over the right to prosecute Mr. Medellin for his crimes affected. His case is essentially no different than that of an arrestee who wasn't read their Miranda rights, as far as I can tell, with procedural violations being at issue, rather than whether the United States has a right to arrest and prosecute Mr. Miranda in the first place.