[Mp4-tech] How to find the multilingual status in AAC audio stream

[Song]

Dear experts,
I am meeting some special AAC streams which have two different language seperately on Left and Right channel. How can I detect this status from the normal streams by my source code? Which syntax element should I check? 
I remember that some old specification define this status as Dual Mono mode. I am reading the ISO/IEC 13818-7, try to find the similar definition, but I have not find the answer yet. Could you please help me clarify this concept?
Thank you in advance,
and Best Regards.
Song
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