Certification is not required to practice law. The attorney may then be certified by the board overseeing that specialty. They are also required to complete three hours of CLE dealing with the ethics of law practice.
Specialization requires additional CLE in the specialty.
Federal courts have their own bars, and attorneys have to apply to be licensed to practice before them. The federal districts in Texas are the Northern, Southern, Eastern, and Western Districts. Appeals from the Texas federal district courts go to the Fifth Circuit. Being licensed to practice in one federal district does not imply authority to practice in another. The federal appellate courts also have their own bar.