The scene is intentionally ambiguous. The woman's dialogue is fast-paced and sounds vaguely Eastern European, but the film doesn't explicitly state the language. Some viewers have interpreted it as Russian, while others have suggested other languages like Romanian or Ukrainian.
Ultimately, the film leaves it to the audience to decide. The ambiguity adds to the atmosphere of mystery and cultural immersion that director Mathieu Kassovitz was aiming for in the film.