The short answer is no.

Language learning not only requires learning to understand the spoken language, but also reading, writing, and speaking. If you were to tune into an online radio station in a language that you’ve never studied, you wouldn’t understand a word that was being said. Presuming that the online radio station was your sole learning resource, you still wouldn’t understand what was being said even after listening for hundreds of hours, because you wouldn’t know any words or phrases in the language which you could use as a reference to pick up more. The best that you could hope for might be making out a few frequently-used phrases like Good Evening.

Even if you made out a few phrases after hundreds of hours of listening, it’s very likely that you still wouldn’t know how to write the phrases. Even languages which use the same or similar alphabet as English often pronounce the letters differently. For instance, the letter j is pronounced with a y-sound in German. Using no other learning resource than listening also wouldn’t teach you the sounds of the letters which have special symbols like ö. And you definitely wouldn’t learn the writing systems of languages which have an entirely different alphabet.

If you want to learn a foreign language, there are better ways to spend all those hours. According to the ACTFL, 480 hours of study can get you to an intermediate level of a language which is closely related to English, whereas 720 hours can get you to the same level in some of the languages which use a different writing system. When there are so many resources that can be used to learn a language, it would be a shame not to take advantage of more of them. Listening to a language is an important part of learning it, but it doesn’t work as the only part.