Malawians Clothes and languages

Hi,
My name is Marie and I am from Canada. I am new on forums...
Lately, we got an opportunity to move in Malawi. I heard there are some clothing rules to follow (like humble and long dresses...), but I cannot find up-to-date info about it.

Does anyone can tell me what they are for both women and men please?

Also, my father would like to know if learning English will allow him to communicate easily with locals too or if Chewa|Nyanja should be added on his learning list ?
Thank you in advance