From the first he was greatly attracted towards historical studies, and this was shown when he began to attend the gymnasium of Oettingen, and in 1782, when he went to the university of Altdorf, near Nuremberg.
Here he came under the influence of the historian, Ludwig Timotheus Spittler, from whom, as also from Johannes von Muller and Friedrich Schlegel, his historical studies received a fresh impulse.
He was occupied chiefly with affairs of the principalities of Ansbach and Bayreuth, newly acquired by Prussia, and especially in the settlement of disputes with Bavaria as to their boundaries.
For the rest, Lang did great service to the study of the history of Bavaria, especially by bringing fresh material from the archives to bear upon it.
He also kept up his activity as a publicist, in 1814 defending in a detailed and somewhat biassed pamphlet the policy of the minister Montgelas, and he undertook critical studies in the history of the Jesuits.