Holy cow, I wrote a book!
One of my friends is fluent in both Mandarin and English.
When she lived in Taiwan,
she paid a visit to a nightclub whose gimmick was that
you had to speak English.
The target audience was not foreigners but rather native Taiwanese
who learned English as a second language.
My friend didn't have any problems with this rule, but
many of the guests appeared to be struggling to conform.
My friend paid a visit to the ladies' room,
and there she overheard a conversation between two other guests.
(They were speaking in Mandarin.
Apparently, the rules aren't enforced in the bathroom.)
"There's this cute guy out on the dance floor,
but I don't know what to say to him.
My English is not very good."
My friend told her,
His English isn't very good either."