The Waverider provides the Legends with a universal translator which allows the team to communicate in any language; in this case Japanese. However the Ray & Nate are referred to as gaijin. Gaijin should have been translated into foreigner.
Nate says that the United States won't exist for another 200 years. The year Nate is trapped in is 1641, so the formation of the United States of America is actually only 135 years away.
There are no safety protocols regarding the ship's outer doors- they can be opened accidentally at any time.
Gideon does not scan the ship for alien lifeforms.