Oakland had acquired Langerhans Sunday from the Atlanta Braves. He went hitless in four at-bats in two games with the Athletics.
Langerhans has struggled at the plate this season, batting .063 in 48 at-bats. He has no home runs and one RBI, and has struck out 18 times.
Washington General Manager Jim Bowden said Langerhans will improve the young team defensively.
"I know late in the game, if we're in the ninth inning and (Austin) Kearns is in right, (Nook) Logan's in center and Langerhans is in left, there's not a better defensive outfield in this league," Bowden told The Washington Post.
The 27-year-old Langerhans is a .242 career hitter in 297 major league games, including full seasons with the Braves in 2005 and 2006.
Snelling, who has also played for the Seattle Mariners, was batting .204 in 24 games with Washington this season.