The speaker is standing in a street, or imagining it, and wondering how one person could possibly fill it with life. The opening question, "might I people the street," plays on the idea of turning an empty place into a crowded one, as if a single man could become a whole crowd. But the next lines undercut that hope: he is "only one man," and all he has is "a translation of a laugh."
That last phrase is the strangest and most interesting part. A translation is never quite the original, so the laugh he carries seems secondhand, an imitation of real amusement or belonging. The title, "Acting casual," suggests he is putting on a performance, trying to look easy and at home when he may not feel it.
The mood is quiet, wry, and a little lonely. There's humor in it, but also a sense of self-consciousness and thin resources, a person making do with very little in a big, empty space.