A new book reviews influences of speaking more than one language.

Language plays a significant role in all aspects of human social and cognitive life. People communicate with each other in a language. The language they speak also structures a number of aspects of the way they think. These effects become even more complex when people speak more than one language. Bilingual (or multilingual) individuals are those who have excellent fluency in two (or more) languages.
A great new book by the cognitive scientist Viorica Marian called The Power of Language explores a number of influences of speaking multiple languages on the way people engage, think, and act. One of the more fascinating sections of the book examines how people think about themselves depending on the language they are using to think about themselves.
If you speak more than one language, chances are you use them in different circumstances. For example, you may have one language that you use at home with family and another that you use at work and in your interactions with people around where you live. You might have a language that you spoke growing up, but that you speak more rarely later in life. You might have a language you speak only in professional situations, but another language that you use in your daily interactions.
These differences in context influence what memories you call to mind when you are asked questions (or ask yourself questions) in the different languages you speak. For example, suppose you speak one language at home and another at work. If you are asked to think about something you have done recently that is fun, you might be more likely to think of an event with your family when asked in the language you speak at home, but an enjoyable interaction with colleagues when asked in the language you speak at work.
The language used to answer the question makes it easier to think of memories associated with using that language. The memories you retrieve in a situation affect what you are likely to do and even how you are likely to feel in that situation.
In addition, properties of the language itself can affect your decisions. In the book, Dr. Marian points out that some languages (like English) require you to use a different tense when talking about events in the present versus the future. For example, if you say “I am walking in the park,” you are talking about something happening right now, but you have to say “I will walk in the park,” to talk about a future walk you are going to take. Other languages (like German and Mandarin) do not require a different grammatical tense to talk about present and future events.
The evidence suggests that people who speak languages whose grammar requires a distinction between present and future are less likely to make choices that benefit their future selves (like saving for retirement) than people who speak languages that do not. Consequently, the actions you take when speaking different languages can have very different implications for your future.
How people think, act, and feel is a significant part of their identity. So, in a very psychologically real way, the language bilinguals are speaking affects their identity in that moment. They are going to be reminded of different experiences. They are going to have different emotional reactions to situations. They may even make very different kinds of decisions.
Interestingly, many of these effects of speaking more than one language can happen without the speaker being aware of them. In the moment, people are engaging with the world in one of the languages they speak. They have no clear way of knowing what they would have done had they been speaking their other language. So, they have no good way to compare their reaction to what they might have done otherwise.
That means that in important situations, bilinguals might want to try asking themselves questions in both of their languages before moving forward. This exercise might lead to insights about ways that their identity is somewhat different depending on the language they’re speaking—and that might lead to different (and hopefully better) outcomes than when they engage using only one language.

reference:
psychology today

link:
https://www.psychologytoday.com/intl/blog/ulterior-motives/202304/for-bilinguals-identity-is-influenced-by-language