Just started showing my 2yo videos of planes when I stumbled upon piloteye.tv on youtube. He's already hooked (hopefully in 21 or so years time he will fly his parents somewhere :-) )

Anyway back to my Q, the videos are mainly LH aircraft, I noticed that the chitchat is in German but when they're going through check lists or given out commands to each other such as engine 3+4 start they say it in English.

is this a requirement to speak in English?