“站有站相，坐有坐相”翻译成英语？

Have a good manner when you stand or sit.

一楼还是可以的， manner 可数，就算有时不可数 a manner 也是常见用法

Be polite whenever you stand or sit.
manner不可数,请1楼注意!

sit has sitting appearance,stand has standing appearance
stand and sit properly

Keep a polite posture when standing or sitting