这只是个非正式的会议，不必穿得太正式。

This is just an ___unofficial meeting, so no need to dress too formally.

这份报告只是非官方的，我们还在等待政府的正式声明。

This is just an ___unofficial report; we're still waiting for the government's official statement.

这次聚会是非正式的，所以穿休闲服就行。

This is an ___unofficial gathering, so casual clothes are fine.