一部电影来看英文

应该正式来说用watch

see a English movie

see a movie（随意些，可能还不确定去不去，只表示有那个意向）watch the film/movie（已经有心仪的电影，比较确定）固定搭配这样比较多见

i'mwatchingamoive

a film

I'mwatchingafilm或者I'mwatchingamovie

you can use both, we are going to see a movie, is used more.

I'mwatchingamovie.