Not sure about that. A signature works too.
We do not know his level of English understanding. Evidence from texts he knows quite a bit. But it would be reasonable after interrogation started to get Miranda in two languages. And signed. These are not amateurs. You have state and federal officials. But i don't think we know their procedure.
Not even sure if the authorities has to interrogate him for some of the information. He could have volunteered all the information, which in case they would not have to read him his rights -- which are read after an official interrogation starts. Custodial interrogation. And of course law enforcement can record and act on information even if it was obtained without Miranda in interrogation. It just isn't admissible in court.
If a suspect runs up and spills information, that's not a custodial interrogation. Only if the subject is detained does he have the right to be silent etc.
Again, this suspect has not been found guilty. He has not been in a trial. So I don't see why he is condemned until he is judged by his peers. That is a basic Constitutional right.
Miranda Rights In Spanish Must Be Correctly Translated, Court Rules | HuffPost