I think I would take this approach:
INT. SUBWAY PLATFORM - NIGHT
Leaning against a wall away from the platform is a DARK MAN, 40s in a long trenchcoat.
Russian agent, VLADIMIR PUTIN, 50s in winter coat and fur hat, descends the station stairway and approaches the DARK MAN, taking a cigarette from a gold case.
PUTIN
(Russian, English subtitle)
There's a full moon tonight. Got a light?
The DARK MAN removes a lighter from his pocket and flicks it.
DARK MAN
(French, English subtitle)
Ripe grapefruit are best with sugar.
PUTIN
(Russian, English subtitle)
Yeah, yeah.
He draws on the cigarette and glances around the platform.
This is a little cumbersome if these are the only people in the scene, however, if a third or fourth were to come into the scene ... say an American or British agent speaking English, you can immediately tell who is speaking what language and what subtitles are called for.