Different ethnics will have different languages to communicate.

 This is one of those situations where the English word has been borrowed and its use altered. In this case what was in English an adjective has been turned into a noun.

English offers two word forms – ethnic (adjective), ethnicity (noun):

• Different ethnic groups will have different languages to communicate.
• People with different ethnicity will have different languages to communicate.

And by the way, how exactly do you describe your own ethnicity? Comments below!