haha,quite simple, if you love that country, or you are interested in the country. Show him or her local food first, you will probably attract his attention. Then it may begin happily.

Try to imagine you will  travel the country that speak the language you are learning, which will bring you motivation. For example, I am learning Spanish by myself, and I know oneday I will visit Spain, when that day arrives, I could communicate with people there in Spanish, which makes me feel so proud of myself.  Additionally, try to watch some movies and listen songs in that language, they are definitely helpful. :)

To make them have any good convincing motivation to start their language learning. Motivation is the king, I reckon. 

advice I can say - watch videos in youtube, there are a lot lessons in it. use program/sites like duolingo, bussu, memrise.....(use here too people always are very friendly to help), watch movies, soap opera, serie in the language you learn. listen radios and podcasts. study grammar, read newspaper and texts about things you like. speak with natives form chats, skipe, ..... listen music and read the letter of music that you like.