Okla. Stat. tit. 5 § 1
No person shall practice as an attorney and counselor at law in any court of this state who is not a citizen of the United States, or who holds a commission as judge of any court of record, or who is a sheriff or coroner; nor shall the clerk of the Supreme Court, or the clerk of the district court, or probate court, or the deputy of either, practice in the particular court of which he is clerk or deputy clerk; but nothing herein contained shall prevent any judge of any of the courts of this state from finishing any business by him undertaken in the district, circuit, or Supreme Court of the United States, prior to his election or appointment as judge; and an alien who has declared his intention to become a citizen of the United States may practice as if he were a citizen.
Okla. Stat. tit. 5, § 1