Answer: Probably 1700s
This would be in the century after LaSalle claimed all the lands drained by the Mississippi River in 1682.
Explanation: I say "probably" because this colonization by Germans is not well-documented in the publications of the Oklahoma Historical Society or the Encyclopedia of Oklahoma History. So I wonder where this question comes from.
One reference in an article about the Heavener Runestone State Park says, "Others contend that the inscriptions were made by a member of La Salle's expedition party circa 1687, or by a Swedish captain leading German colonists as part of a French colonization effort in the Mississippi Valley between 1718 and 1720."
Other articles mention of Spanish settlement in areas claimed by France.