We tend to believe that our identity is something fixed and relatively stable. It may be more accurate to view identity as flexible and shifting, depending on where we are, who we are talking to, what we are talking about, and so on. My identity shifts to some extent when I move from a university meeting to a family dinner, for example. I become less formal, more expressive, use gestures/nonverbal communication more, and so on.
In my English speaking identity, I have a much larger and more varied vocabulary. I shift into more sophisticated vocabulary if I want to create distance or put someone down (which I don't do very often, but there have been times I've corrected a native speaker on fewer/less, lay/lie, and so on). (ok and yes, I correct "Columbian" coffee to "Colombian" every chance I get).
If I want to swear, it's in English. Profanity in Spanish is quite dependent on which variety or country you are in, and I don't really know much anyway. Besides knowing swear words in English, I have a much stronger emotional connection to swearing in English. I had an Israeli student once who said she talked to her daughter about sex in English because she didn't feel embarrassed as she would have in her native language. It's just more fun to swear in English.
I tend not to use a lot of gestures in English. I am reserved, shy, quiet around people I don't know well. I love hearing new accents and speaking with learners of English.
In Spanish I am more outgoing. I use more gestures. I talk more and worry less about not knowing someone. I can shift formality but in spite of a good vocabulary, I can't really use my words to signify a change in attitude.
And there are some things I can say in Spanish that I have to work on to say in English.
Encimar: add something on top. So if I spend a lot of money someplace I might ask if they will "encimar" something for me. In English I'd have to ask if they will add something on top for free because I just spent a lot of money. Hmmm.
Estrenar: show off something new. As in "are you estrenando that sweater?". In English....are you wearing that sweater for the very first time and showing it off?
Malcriado: badly brought up, as in being rude, not knowing appropriate social cues, really a bad thing to say about someone. In English I'd have to say what a badly raised person but you miss all the additional meanings.
And all the "que" expressions, so lovely. Que espantoso! Que cosa! Que malcriado! I guess I can say how scary, what a thing!, what a badly brought up child! You can use just about anything with "que" and have a satisfying comment.
So while perhaps trivial, all this leads me to think about language loss or maintenance. I say losing a language is losing a culture. What can you say in another language that you can't say in English? How do those expressions reveal a values and belief system (I believe you should add something free to my large purchase because we are helping each other). Who is your English persona? your second language persona?
Culturally, the USA tends to be highly individualistic. Most Latin American countries are more collectivistic (as are Native Americans and Japanese). In my Spanish guise I recognize and appreciate that it isn't the house or apartment, it is the people you spend time with. In my English guise I love my private house, hate unexpected visitors, and feel safe and comfortable. So my values shift to some extent. I like children better in Spanish, too!
Having more than one language means we have a wider world view, can see issues from different vantage points, pick up on shades of meaning, and understand our native language and culture better, since we can see it from the outside.
I worked hard (and am still working on) learning Spanish. I treasure it. Children, however, can learn second and third languages with the same facility they learn their native language. Yet our school systems (and sometimes parents) seek to eradicate any language other than English. And then in high school we require them to study a new language. Where is the sense in that? Glad to see that my local school system is finally beginning immersion programs, in Spanish and French (we have Congolese refugees). Europe has encouraged multilingualism for years. Because of our geographical isolation, we haven't apparently seen the need or value. It's time for that to change.