Go somewhere you don't speak the language, move somewhere that scares you a little
If you can swing it, give yourself six months or a year somewhere with a different language and a different culture. Immerse yourself fully. It opens your world in ways you cannot predict from the outside.
I moved to Cancún at 25 not speaking a word of Spanish. The first six months I understood almost nothing. But eight years later, Spanish was just another way of thinking to me. You stop being a visitor and start being a person. That is what immersion actually does.
In Granada last year I ended up in a 40-minute conversation with an older man at a tapas bar in the Albaicín because I could actually talk to him. He told me about a mirador locals use to watch the sunset over the Alhambra that almost nobody knows about. That conversation changed my entire day, and it only happened because I could have it.
You do not need to be fluent to start. Even 20 phrases will change how people interact with you. "Please, thank you, excuse me, the check please, do you have a table, where is the bathroom?" That covers 80 percent of what you need. Download the Google Translate offline pack before you go. It has saved me more times than I can count.
The biggest advantage of speaking multiple languages is not the words. It is the cultural fluency that comes with them. When you speak someone's language, you understand their humor, their rhythm, their values.
So pick a place. Pick a language. Get out there and travel.
What is your story? How did you learn?