In india, the 'common language' that is used when 2-3 other languages exist that all might not know diffrs with the region. In the south, it is firmly English. From Maharashtra up, it is Hindi. In India such a 'everybody understands' language is necessary with 15 official languages. I read somewhere that in switzerland it is not so. The Swiss speak to each other in their own language - German, french or Italian. That makes a lot of sense. It is easy to understand the other language and easier to speak your own.
Is there a word for this "pan lingua language"?