Language and culture are closely related. To learn a language thoroughly it really helps if you become familiar with the culture of people who speak it. If you haven’t grown up in that culture there will probably be things that seem unusual or strange to you, but there will be just as many things in your culture that seem normal to you but are strange to people from other cultures. There are probably many things you learnt while growing up that you take for granted and assume everyone knows – these are the kinds of things that help you become familiar with another culture, and to become really proficient in the language associated with it.
For example, there are probably songs, rhymes, poems and stories you learnt as a child that most people in your culture know. To become familiar with the equivalent songs for a different language and culture you could read children’s books and use of materials for children. You could also ask any people you know who speak the relevant language to teach you some of the songs, stories, etc they learnt as children. People tend to remember such things well, although they may need some prompting, and will probably be happy to help. There might also be books of popular songs that most people who speak a particular language know.
Learning these things will not only help you understand a different culture and improve your proficiency in the language, but you will also really impress people if you can sing along with their popular songs, recite their poems, and/or tell their stories.