I don’t think there’s a skill as useful and fun to develop as a second language. I think the process of expanding your vocabulary in your target language as well as finding new ways to commit to memory what you’re learning is not only great for cognitive development but it is also enjoyable!
With Dual Educates I’ve been learning Spanish and loving every second of the process. I’m now much closer to the level of fluency that I want than I was a few weeks ago when I started learning, and I can confidently say I see myself getting to where I want to be with my level of Spanish in just a few more months!