The internet is English friendly. Most educated South Americans speak English, and you need English to learn advanced science.etc. because that is what the text books are written in.6
as for Mandarin...one third of Chinese do not speak it, and many who do speak a dialect that others may not understand. Most if the Chinese diaspora speak Cantonese...Then there is the problem of writing Chinese.
Chinese is far and away the most common language, in the world.
Mandarin and Cantonese is not a clear distinction, since many actually speak both.
Written Chinese however is constant among the entire country, and among all Chinese everywhere. With the exception, that there are more complex characters used in Taiwan and away from China, than the slightly more simple characters actually used in China.