Does the lawyer of the company need to send a letter from the law firm when he appears in court?

Yes, to appear in court as a lawyer, you must have a letter from the lawyer where the lawyer is, plus a copy of the lawyer's practice certificate. Lawyers do not appear in court as lawyers, but need to appear as company employees, such as company legal affairs, and need to appear in court with company contracts. Lawyers don't usually do this. Strictly speaking, not appearing in court as a lawyer will be considered illegal.