In my opinion a name should stay the same in every language. A name is not something you should ever try to translate.
Why not "Big Matthew"?
Because John Cena is John Cena and not Giovanni or Jean Cena.
The Tips and Notes explain that in order to keep the course accessible, only the Czech forms of the name would be accepted, as Matěj, could have many forms in English or Other European countries: Matthew, Matt, Mats, Matthieu, Mateo...
Why do we hear MaKey?
Please review the Tips and nores od the first two skills about Czech orthography and pronunciation. T followed by Ě is Ť.
Matěj, what is? Name?
It's a name. Translated to English, it's "Matthew".
Маттяй) I think the Russian equivalent is "Motvei" (Мотвей)