1. I am for swimming this vacation.
我赞成这次休假去游泳。
还能这样说：
I agree with the idea to go out for swimming this vacation.
I favor swimming this holiday.
应用解析：
for all 尽管，虽然；
be for it 惹出麻烦；
but for 如果不是，如果没有；
for sb. to 使某人做某事，应由某人做
2. Come for a swim.
来游泳吧。
还能这样说：
Would you like to swim?
Do you want to swim?
谚语：
Good things come in small packages.
好事多磨。
3. Swimming in the lake is forbidden.
禁止在湖里游泳。
还能这样说：
You can't swim in reservoir.
You are not allowed to swim in the lake.
应用解析：
forbid sb. to smoke 禁止某人吸烟；
forbid sb. the house 不准某人进屋；
Parking forbidden! 禁止停车！
4. My father is teaching my sister how to swim.
我的父亲正在教妹妹游泳。
还能这样说：
My sister is learning to swim with my father's guidance.
My father is telling my sister how to swim.
应用解析：
swim over 从……上滑过；
go for a swim 去游泳；
be in the swim 熟悉内情；顺应湖流；
sink or swim 不论成败；无论如何