I would like to know if there is a technical (or common) term for the type of bilingual (or multilingual) conversation described in the title. For example, one person could be speaking French, while the other is speaking English, while understanding each other. This could happen if both speakers have studied the other language enough to understand it, but not enough to speak fluently. In a different situation, this could also occur between two languages with high mutual intelligibility (perhaps Spanish and Italian, or some pairs of Slavic languages), without the speakers having specifically studied the other language.
The same idea was hinted at in this earlier question, which didn't get much discussion.