Skill not concept.
Language is a skill just like Kong Fu. you needs to use the skill that mean basic ,If not use it will be forgot ,in the English the hardest part is not take in knowleadge but is use knowledge to outside world and our life ,this is hardest part. Many people don’t know how to use it , so do I.
This If we want to switch language in our life without think about it, you must use in to the daily basic. This is the only way we can switch our brain language fnctions.
Use it or lose it mean , when you remenber you must use otherwise will forgot the knowledge. Right now I use English a lot in the school at home and I forgot the my mother tong how to write that I need to do research ,because I already not use chinese since 2017 . Crazy right ?
So don’t forget to use it ,use more know more , yes or yes?