People are different people when using different languages. Studies show that people think differently, behave differently and even have different morals. One example is to compare now you feel when saying, “I love you,” with saying, “Wo ai ni” or the equivalent in your own tongue. In your native tongue, it feels much more personal and more heartfelt than in the foreign tongue. It’s not just in the head either. It is a measurable effect, with sweat, faster heart rate, dilated pupils in the eyes and so on.
Each year I show the above video to my students as part of one of my classes. In the video, we have 25 people, each saying, “I love you” in their own language. The students enjoy the video but sit quietly through most of it. That is until the Chinese person comes on. At that point, there is always a laugh and a giggle in the class. At first I thought it was because of the big furry hat the Chinese man is wearing, but actually, quite a few other people in the video have odd clothes, stick out their tongues and dance about. The reason the Chinese person got a reaction is because he is speaking in my students first language. They feel an emotion with that man that they don’t feel with any of the others. Even when the others speak English and the students understand it, they don’t get any emotional connection from it.
If your wife often says, “Te amo,” to you (Spanish for, “I love you”), then you build emotional connections to that phrase. So that phrase has meaning to you beyond just being a set of words that you understand. If your wife says the English, French or German words, then it won’t trigger the same response because those words haven’t the same learned connections to the emotion.
The studies I read say that it is not simply fluency. The brain handles language in a complex way. Your primary language functions within a different section of the brain from your secondary language (except in those who are bilingual from birth who use the same part of the brain for both languages). Other parts of the brain handle the translation/understanding and control responses. When you hear something, the relevant part of the brain takes it in, interprets it and then various parts of your brain create responses to that input. If you often you hear something and have the same response each time, your brain starts to grow connections to that response so that it happens faster.
These responses can be very particular for a certain sound. For example, a parent will wake up sharply to the sound of their child crying but sleep through someone else’s child crying. The particular sound of your child triggers responses while a marginally different sound with the same meaning has a reduced response. The more you hear a phrase and react to that phrase the strong the reaction gets. Thus when growing up, you connect all sorts of emotional responses to phrases in your primary language. The connections between the section of your brain that handles the primary language, and the section that handles the response, grow, expand, become stronger and faster.
The secondary language, however, is in a section of the brain that is less well linked. When it hears a phrase, it is slower to pass it on to the responding areas of the brain. It might well pass the message to a completely different area from what the primary language processor did.
You can demonstrate this with experiment. Consider the following experiment for you to try. Pick a passing stranger and just say the Russian, “Я тебя люблю” to them. Then repeat with the Spanish, “Te amo”. Repeat again with English, “I love you.” You could go on with any other languages you know. Repeat with many strangers of different ethnicities and sexes. Here it is you saying it, so your fluency of understanding the words has zero influence. You understand what you are saying perfectly before you say them. However, you will feel more reserved, more abashed, more brazen, more confident, or shyer, in one language rather than another. It is the words themselves that trigger an emotion rather than the understanding of the words.