Learning a new language is much more difficult as an adult, and you'll never speak it like a native if you pick it up after your teenage years.
Some people have more of a knack for it than others. If you find the process of learning new words and phrases fun, you won't lose the motivation. You should find something fun and enjoyable to listen to or read in the target language. For Spanish it could be dramatic soap operas or interesting travel videos. For Japanese, it could be anime or manga.
As we move into a more decentralized world, knowing the local language of the country you're staying in will likely become more important.