Within Gainsbourg’s career this sounds to me like a stopping point between the sharp pop songs he was writing for himself and others in the 60s and the more drawn-out, high-concept records he made in the 70s: “Je T’Aime”s bass-heavy langour could be a practise run for bits of 1971’s terrific Histoire De Melody Nelson. If it wasn’t for the bass, in fact, “Je T’Aime” would be a pretty dire record – neither the somewhat prissy string arrangement or the soft-focus blur of the organ have aged that well, but the bass makes the song work as an insistent slow dance.
Precious few of its ’69 listeners would have worried much about Gainsbourg’s career (though rather more would have cared about slow dances) – in the wider pop world he was just an archetypal filthy Frenchman, one enthusiastically living up to that archetype by debauching a fluttering English rose. Actually Birkin’s performance is much better than Serge’s – he is on gravelly seducer autopilot, whereas she gets the harder job of coming on record while still carrying the tune (her stabbed “viens!” and “reines!” at the end show how well she does it).
Few foreign language songs get to number one in Britain – this one was helped by radio ban controversy and a bottleneck in the single’s availability. But foreign language hits in general weren’t unheard of in the 1960s – Eurovision winners in whatever language tended to do alright, for instance. In the case of “Je T’Aime”, the language barrier must have helped sales by making the track more viable as a romantic record, as well as preserving its porno mystique.