Estonians speak Estonian as their native language.
German is not the official language in Estonia, but some Estonians surely know how to speak German.
Georgians speak Georgian as their native language.
Serbians speak Serbian as their native language.
In terms of native languages, 76.54% of Turks speak Turkish as their native language, 20.2% speak Kurmanji Kurdish as their native language, and 1.38% speak Arabic as a native language.
Navajos still speak their native language. They also speak English.
English is the official language of Nigeria therefore it is their 'native' language.
The native language of Albania is Albanian.
Grapes speak Esperanto as their native language.
You should always speak the common language of the place you work. If your native language is different than the common language, it is counterproductive and rude to speak it at work.
Native Americans speak in language not in symbols.
For the same reason you speak English. That's their language. (However English is not your native language, I think)
The majority of Brazilians speak Portuguese as their native language.