I'm a chinese,but I'm learning English now.Sometimes,I even speak English better than Chinese. My country tells me to learn the most common language well,I did it.but now, SometimesI forget that how to say sentences with Chinese.Diffierent cultures mak diffierent languages.How do we learn then?
啊，sometimes it happens to me too. If you want your mother and second language to be balanced practice will be needed. That is how a person that knows many languages maintains its languages at a certain level. Also I think you have focused too much with English, hahaha. This is all in my opinion. You can try researching if you want.