I don't think that a child who learns a new language will lose their cultural identity, because the purpose of learning a new language is to understand the world better. The diversity of different cultures is just like the bright-coloured flowers in a garden. Each of them has their own features. If you are narcissistic and look down on others, you will definitely be isolated by others. So, a language is a tool to have a conversation with the rest of the world. You can find something different and interesting from your culture. You can be proud of your culture while admiring some great things from other cultures. I never say which culture is the best, I say that every culture has their advantages. Kindness, patience and love are the most acceptable traits throughout human history. So, the cultures which centre around these human traits are worth learning about.