Ciro Santilli By writing in English you reach more people.
Writing in any other language is a waste of time.
The reason is simple: English speakers control a huge proportion of the world's GDP.
English is the de-facto Lingua Franca of the second half of the 20th Century, it is the new lingua franca, the new Latin, and there is no escaping it.
Students who don't know English will never do anything truly useful in science and technology. So it is pointless to teach them anything (besides English itself).