How do you say in English that I want to go to the toilet when I am unaccompanied?

In an environment where you can communicate in English, you don't have to apologize if you want to go to the toilet, just tell the other person directly:

In public places:

Excuse me, I'd like to use the restroom. I'll be right back.

Visiting a friend's house:

Could I use your bathroom, please?

Could you show me your bathroom, please?

In the workplace, among colleagues:

Just sec, I'm gonna use the restroom. I'll be right back.

excuse me, i need go to washingroom.

Excuse me, may I be excused for a minute。

This is often used in reality, and it doesn't need a literal translation that I want to go to the bathroom.

I'm sorry/Excuse me,but I'd like to go to the washroom...

Just say Excuse me is fine.

Excuse me

I want to pick some flowers.

This one is very subtle.

Excuse me, I want to go to the washing room.

Excuse me, I've got to wash my hands.

It's okay to just say excuse me upstairs.

Excuse me, I want to answer the call of the nature.

sorry,to the washing room!