The answer to this question, sadly, is a resounding yes. The process even has a name; ‘language attrition’ and is defined as the process of losing a native, or first language. This loss is generally due to isolation from other speakers of your native language, i.e through a move to a different country, as well as the introduction of a second language.
The process of language attrition is much more common in children. If you have learned your native language fully from childhood and speak it up until you are around 12 years old, this language will normally be quite stable and difficult to erode. This doesn’t mean you wouldn’t experience any symptoms of language attrition if you were to move to a new country and begin to speak a new language, but is it unlikely you would truly forget your mother tongue. However, if a child is moved from the native community before the age of 12, when language has stabilised, it is definitely possible for them to forget their first language to a large extent, or even entirely.
Language attrition occurs because two languages are competing for mental resources. For example, when an Arabic speaker begins to learn English, that person has to put quite a bit of mental energy not to use an Arabic word or Arabic sentence structure when they are speaking English. When they need to focus on a specific English word, they have to mentally block the Arabic equivalent from their brains. When they then want to use that Arabic word again, they have to put further effort into overriding the mental block that they have put in place. Monika Schmid, the leading researcher on language attrition currently based at the University of Essex, explains that “it’s not that you’re forgetting a language, what is happening is that it has been buried and you have to dig it up again and that takes quite a bit of energy.” However, the total loss of a native language in children comes when they don’t expend that energy to remember their first language. If they totally stop speaking their first language, or even speak it with less regularity than their second language then they will likely substantially or totally forget it.
However, there is some evidence to suggest that the language we learn at an early age leaves some kind of trace on the brain long after it is believed to be completely forgotten. A 2014 study found that Chinese children adopted at 12 months by French speaking families in Canada were able to respond to “Chinese tones”. The studies consisted of girls between 9-17 who were split into two groups. Group One were girls who only spoke French and had never been exposed to Chinese. Group Two consisted of bilingual girls, who spoke both French and Chinese, and Group Three was made up of Chinese adoptees who only spoke French. All groups listened to “pseudo words” that used tones found in Chinese languages. Interestingly, this study found that the bilingual girls AND the adopted girls (who had been exposed to Chinese in early years) had the same brain activity when listening to the pseudo words.
However, Schmid notes that although there is evidence that native language is able to stay with children in some strange way, this doesn’t necessarily mean that such children would have an advantage if they decided to relearn their forgotten language. She concludes that, although the child may be better than their peers at pronunciation with no prior knowledge, for grammar and vocabulary the advantages would be minimal. “There are a few neuroimaging studies trying to find residual knowledge through brain scans, but they, too, show that if such knowledge exists at all, it is very subtle and probably will not be very useful for the purpose of re-learning.”
One of the most interesting things about language attrition is that the most important factors to retaining a language seems to be how you feel about the language. Emotional connection to the language appears to have more impact on level of language attrition, more so than more obvious factors such as age at time of emigration and amount of use of the language. Studies have found that a positive attitude towards your native language can help with its maintenance, and a negative one cause and speed up attrition. This was most evident in a study of German-Jewish refugees, where a clear link emerged between the amount of Nazi persecution individual speakers have suffered and the amount of loss they had of their first language. Refugees who thought sentimentally about the German language, as it was the only thing their parents had given them that the Nazis had not been able to take from them, had much less evidence of language attrition. Refugees who viewed German as the language of their persecutors and therefore despised it, had a much more extreme level of language attrition.