Word when two people use two different languages in a conversation [duplicate]

Is there a word that describes or denotes a type of conversation in which two speakers speak two different languages.

In our country, Pakistan, there are approximately 75 languages, from which Urdu, Punjabi and Sindhi are common, excluding English.

So today I found two women speaking two different languages. For example:

Speaker 1 has Urdu as their mother tongue.

Speaker 2 has Sindhi as their mother tongue.

Speaker 1 and 2 spoke their own mother tongue, which are different (Urdu and Sindhi) but both can understand each other's language.

I thought that this is known as "intermingling conversation," or a "code switching." In my opinion, we can't use such words because code-switching refers "shifting completely to the other language for a word, a phrase or sentence, and then revert back to the base language."

Example sentences:

• They were in a bus and had [adjective] conversation.

• They were in a bus and had [noun or noun-phrase for such conversation].

I agree that the question (which is suspected as a duplicate one to this question) is really a duplicate, but its single answer still doesn't satisfy all. In that question, the phrase "bilingual dialogue" was suggested, which I (and others may) think that this refers to the code switching as well, which I don't want here. Some words confuse the readers which sense do they mean.

I would also love to quote the comment of @Lambie regarding the term "bilingual" over here:

"Bilingual refers to one person. Not two people each of whom has a passive knowledge of the other's language but do not speak it well enough to use it actively."

In his book Talk in Two Languages, Joseph Gafaranga examines, among other things, the patterns of conversation within bilingual families. He calls the pattern described in the OP's question the parallel mode. Here is a screenshot from Google Books of the introduction to his discussion of the parallel mode pattern.

https://books.google.de/books?id=-PrMCwAAQBAJ&dq=parallel+language+conversation+garafanga

So by Gafaranga's terminology the Urdu and Sindhi speakers were conducting a conversation in parallel (language) mode.

I believe the most accurate word you'll find for the conversation itself is "bilingual." As in:

The two ladies were having a bilingual conversation

However the inability of the two speakers to fully command both languages is a property of the speaker, not the conversation. The term for this inability is "receptive bilingualism." You would need to change up the syntax a bit to clarify the situation:

The two ladies were having a bilingual conversation, however both were only receptively bilingual in the other's language.

"Passive speaker" is another way to refer to this type of speaker, however this could also imply that the speaker is simply non-aggressive in their speech.

One term that comes up in this context is cross-language (or cross-linguistic). I haven't found a formal definition for this term, but it is fairly transparent. It collocates with "mutual intelligibility" (see below) but also appears in contexts where, for example, the participants in the conversation are employing an interpreter. A couple of examples of use (bolding added):

[W]e aimed to assess the cross-linguistic intelligibility between the related languages as it is in actual practice, i.e. including the effects of the participant’s education. Our study therefore offers an overview of the cross-language intelligibility between related languages . . . .

—Charlotte Gooskens, Vincent J. van Heuven, Jelena Golubović, Anja Schüppert, Femke Swarte & Stefanie Voigt (2018) Mutual intelligibility between closely related languages in Europe, International Journal of Multilingualism, 15:2, 169-193, DOI: 10.1080/14790718.2017.1350185

People using Skype or web applications can now have a cross-language conversation, each speaking in a different language.

—"Real-time Speech Translation in 23 Languages for Business; ReadSpeaker Adds Text-to-Speech Voices to Translate Your World's Voice-to-Subtitles Software", Monday, November 26, 2018 (press release)

Another potentially relevant term is mutual intelligibility. From Wikipedia:

In linguistics, mutual intelligibility is a relationship between languages or dialects in which speakers of different but related varieties can readily understand each other without prior familiarity or special effort.

Note that in linguistics "mutual intelligibility" generally¹ refers to inherent characteristics of the languages, rather than special knowledge on the part of the speakers—that is, it's usually used for related language "pairs" like Portuguese and Spanish or Swedish and Danish,² but generally wouldn't be applied to, say, an English speaker who knows some Mandarin and a Mandarin speaker who knows some English speaking to one another in their own languages.

With that caveat, I think the adjectival form, mutually intelligible, could be used for your situation. The plain meaning of the phrase is fairly transparent and would seem flexible enough to encompass the English/Mandarin situation described above, particularly as it is also used in non-linguistic contexts to describe communication and conversations. Some examples of use, both technical and non-technical (bolding added):

"Are Urdu and Sindhi mutually intelligible languages?"

—Yahoo Answers question (opinions in answers are mixed)

In my experience of observing Spaniards and Italians talking in their respective languages to each another, it is possible for them to have a mutually intelligible conversation as long as they speak clearly.

— Conor Clyne, "How different or similar are Italian and Spanish?" Tsar Experience, August 25, 2016 (blog entry)

Whatever the differences between the Stoics and the Christians, they can be put into mutually intelligible conversation.

—Christopher Kavin Rowe, One True Life: The Stoics and Early Christians as Rival Traditions, 2016

So for your example, you could say something like

• They were in a bus and had a mutually intelligible, cross-language conversation.
• They were in a bus and had a cross-language conversation.
• They were in a bus and had a mutually-intelligible conversation in Urdu and Sindhi (respectively).

¹_{"Generally" only because I've seen some suggestion that sociolinguistics occasionally use it in a different sense.}
²_{See the May 28, 2014 Language Log post "Mutual intelligibility" and especially its comments for an informal discussion of the degree of mutual intelligibility of dozens of language pairs.}

It has been called code-mixing in academic papers.

Code-mixing is the mixing of two or more languages or language varieties in speech.

Wikipedia