To promote a product, which language would be in effective Ad? (a) local language,(b) international common language,(c) both languages?

Marketing ad.
for a products is targeted mainly on consumers locality, culture and language.
If the products marketed in local market then marketing Ad.
would be best in local language.
If the products marketed in different market at different country then marketing Ad.
would be best in international language.
But when a product popular both in local and international market then marketing Ad.
would be best in both local and in international language.
Using two language at a time in common Ad.
will save additional cost for marketing Ad.
and at the same the promotion of the product will rise among vast people.
 

I support for local languages so that each area has their language so that they can understand well and the product demand will be grown up !!!!!

The local language is the consumer language.

Depends on your target group.
For old people usually local language.
For young people you can make a mix.
Begin with the local language and finish with a slogan in a foreign language.
Youan see it in sport brands , etc.
they use English slogans & images.