I've watched a Ted talk on website. The speech was given by a speaker who named  Patricia Ryan. 

I found there is a sentence that I got a bit confused. There is a part of transcript.

"No longer just a foreign language on the school curriculum, and no longer the sole domain of mother England, it has become a bandwagon for every English-speaking nation on earth."

question 1: what does bandwagon mean in the sense? (Does the term refer as 'trend' ?)

question 2: why she said " the sole domain of ...." (Does it mean she want to being respect to own country?) 

Thanks in advance!!

I'd watched English drama to improve vocabulary, phrase and slang. However, there are a whole lots of daily conversation sentence that I don't understand. This is one of them.

As the following, I put on a clip of conversation.

A: I think there is a girl spying on us.

B: dark wag? button nose? 

A: Yeah

B: Don't acknowledge her.

The person was replying don't acknowledge her. Dose it means to snub the girl  or be indifferent to the girl?

Can you compose  sentences including acknowledge for me?

Thanks for your help:)