In malaysia, malaysian chinese might speak malay, english, their chinese dialect and mandarin.
In India, marriage among different linguistic groups is very rare. Majority of the Indians generally tend to be monolingual, especially in villages. some of them might be bilingual or trilingual. A tamilian might speak tamil alone, sometimes english too. A malayalee might speak malayalam alone, or english. Most of them speak their respective state language alone. If they happen to live in borders, they might speak an additional language. Less than 10 % of indians might speak four or five languages. A majority of these multilinguals are bad at writing in languages other than mothertongue.
Learning four languages is very difficult. If all the languages are in same linguistic family, it is comparatively easy to learn.
If all of them belong to different families, (father- chinese, mother - tamil, country- japan, foreign language - english) it is very difficult.
Generally, the parents' mothertongues are ignored.
1. Both of them tend to speak a neutral language to the child. (may be the country's language)
2. The parents language doesnot have much to do with the culture of the country or it doesn't have anything to do with jobs.
The local language has to be taught first, since it helps to mingle with the society.
Even if more than three languages are taught, it is very difficult to learn with high fluency.
However. in places like Bangalore, most people happen to speak 3+ languages due to the interaction with other communities living in the surroundings.