Racially discriminated at Rink's Gun & Sport near Chicago Illino

 
Yesterday I took my in laws to Rink's Gun & Sport. I want to introduce shooting this very American sport to them.
I walked in and ask to use the range, the front cash register clerk pointed me to a register near the range door.
There the clerk asked me if I want to use the range and I answered yes.

I took out my wallet and ready to pay, my wife walked in with my kids and asked me in Chinese: “孩子要peepee，你问问厕所在哪里 (Kids want to peepee, please ask the clerk where the restroom is.”
Totally unexpected, the clerk yelled at my wife: "English Only！”
“what？？？” Me and my wife were shocked and looked at him, kids were scared。
I said：“I can speak whatever language with my family."
The clerk said in a very rude tone: "Not in my store."
I said: "You want English? I have an English word for you, FUCK YOU!"
The clerk said: "Fuck you."

The manager heard our argument and asked me what happened.
I explained what happened, and the manager said: "This is America, you need to speak English. It's our policy, it’s on the door."
I said:" I am American and I can speak whatever language I want to speak, especially with my family."
...

Kids are scared and my in laws are very nervous. Me and my wife were really mad.

We walked out and look at the policy and I took a picture. 
I told the manager, I will let my lawyer talk to him, this is not ending like this.


After coming back, I talked with some friends who knows the law, apparently the chance to win is quite small if I go to court. 

But I have been thinking, what if I bring someone who is deaf, who only use sign language, so this deaf can't be in their store?
Someone like my mother in law who is American citizen but speak very little English, can't be in their store with a translator?

My kids are scared and got the impression speaking Chinese is going to getting them in trouble, I now need to take them to see counseling. I always told them Dad is very proud to speak three languages English, Chinese, and Russian. And I hope them to be bilingual at least and maybe speak three or more languages. 

My fellow brothers and sisters, anyone with legal experience, please help me with advice.
Even with small chance to win, I am taking them to court. 
I am going to show them who is the real American.