1) Which system languages should they include in their ROM for Malaysia?

ENGLISH & MANDARIN

2) Which language should be the default, and what is the order in which they should display them all in the startup screen?

ENGLISH of course

3) What other features do u expect should come with Xiaomi phones?

highly rootable and developer friendly, run pure aosp rom like nexus device, with higher spec than nexus device. then it's a instant win for me. also price between 1500 - 2000. for a unknown brand here, they got to be priced aggresively