When my daughter was three she spent a few months in China. At her age she was able to absorb the Chinese language and had gotten to the point that she no longer spoke English. Within a few weeks of returning to America, she recovered her English and soon had forgotten what she had learned of Chinese.
We, her parents, wanted her to maintain her second language but it was a struggle that we lost. She had no interest in speaking a language her friends did not and saw no value in the effort required to stay fluent. The ability to speak to her family in China, the few times she got to see them, didn't have enough personal value to her it seemed.
I wonder just how much language shapes the person that speaks it. I've read stories that claim entire cultures are reinforced by the language used. That concepts with no words are not discussed and therefore are excluded from thought. I think that even with American English being an agglomeration of words from the languages of the American immigrants, mass media has consolidated it. To a great extent, we Americans seem to have lost our regional accents. Even those tended to help differentiate groups of people and give a local sense of who they were. Words have meaning beyond what a dictionary says. Not only from slang meanings but also from the context where, and when, they are used. For the person that says or thinks them, a full spectrum of related meanings are attached.
Today, I was listening to the radio and an interviewer was talking to a Cuban immigrant. He explained that he felt that his soul had been split because he had been forced to speak two languages. The associations that he had with people, places and things echoed in the words specific to the language that he had acquired them in. He said that he could only fully express himself by using both at the same time.
My daughter did not want to feel different from her classmates. Speaking a language only a few of them knew would have separated her from the rest. In my opinion, spending time with only a small group of her peers, so that she could maintain another language, would have changed the person she has become. It would have built a vocabulary of experiences that only that small group would truly understand.
I feel that being able to speak more than one language allows a person to express more ideas than are traditionally available in a single one. However, knowing words that others don't can intimidate them.
So when people say, "Learn our language", I believe they are actually saying, "Make us comfortable by speaking like we do."