If God wants to give a particular experience to an individual, then God will enable that person to see an angel with his human eyes. Otherwise, we have to use our intuitive vision. It can also take place in a dream. Sometimes when people dream, their intuitive vision is unconsciously functioning and they can see angels. On another level, sometimes, when God wants to manifest in and through someone, he will give that person an angelic touch.
Love is the current that lifts an angel.
Angels have their own language. It does not sound like an earth language. Angels can often help you see things in a better light. Some angels come from a higher planes than others. They try to help mankind.