Someone who learned English, Is it possible to think in English this person? to be like mother tongue or like a baby born in America.
closed as off-topic by Mr. Shiny and New 安宇, Hellion, Fraser Orr, tchrist♦, Drew Nov 10 '14 at 23:16
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That very much depends on the person and can vary from day to day and language to language even for specific individuals, but generally the answer for most people is no, at least not completely.
One very common phenomenon among non-native speakers of any language is called code-switching. Code-switching is when a speaker unintentionally switches between two or more languages when speaking. Code-switching happens because language acquires a very foundational place in a person's mind from a very young age. If you learn to see and interact with the world in, say, Spanish terms (la boleta, la vaca, el tiempo) as a native speaker of Spanish, then go on to learn, say, English as an adult, you might sometimes find yourself inadvertently starting a sentence in English and finishing in Spanish: "I can't, I need to go to la tienda."
Code-switching is a symptom of the way language works as a filter for a person's perspective. From your earliest days, a great many things in life have been taught to you through written or spoken word, so when a Spanish speaker thinks of una cerveza, una cerveza is una cerveza, while for an English speaker, una cerveza is the Spanish word for beer. Similarly, for the Spanish speaker, beer is just the English word for la cerveza. Because your first exposure to so many things in life is typically rooted in your native language, the word for that thing in your native language develops a special place in your mind as the name for that thing. Other language's words for that same thing are just labels, after a fashion--you can call una cerveza a beer, or you can call it una birra or une bière or ein Bier, but to your mind, all those words from all those other languages will always just be a different way to say una cerveza.
Reading up on code-switching can give you a unique insight into this psychological aspect of language learning. Just search for "linguistics code-switching" without the quotes on Google, and you'll find a wealth of information on the topic.