The poem opens with an unpleasant picture: a barrel of stinking water, carried on a barge toward a new ship. Nothing is said about who owns it or where the journey began. We just see the cargo, foul and ordinary, being moved from one vessel to another.
Then the speaker steps in with a single line: "I have translated my life in three lines." The image becomes a comparison. The speaker's life is the barrel of old water, something stale or unpleasant, shipped on to a new vessel. The three lines are the barge and the new ship, a way of carrying a life across into another form.
The title, "Gained in translation," twists the familiar phrase "lost in translation." The speaker suggests something may be gained, even if what's carried over smells bad. The mood is wry and quietly self-mocking, with a hint of acceptance. The poem seems to say that squeezing a life into words is crude and a bit absurd, but it still moves the life forward.