It is a common that a significant number of foreign anime viewers have all been motivated to learn the Japanese language. I will not deny that anime (along with manga, music, video games, dramas and movies) was my foundational motivation as well. For some people, it just sounds cool, dramatic, and brings a more immersive experience. And there are those that wish to visit or live in Japan in hopes of being able to communicate with the locals.
I am sure if you’ve watched enough Hokuto no Ken, you could probably pick up the famous tag line of “omae wa sude ni shinde iru,” or “you’re already dead” after over 100 episodes. Or if you have watched Prince of Tennis, you probably already know “mada mada da ne.” In addition, since the days of VHS fansubs from the 1990s, the suffixes of san, kun, chan, sensei and sama have been included with the character’s names if they are at all used. So I am sure many of you reading have managed to to pick up these simple basics.
Then there are also those within the fan base and more academic oriented Japanese language learners (whether they like anime or not) that discourage it for reasons ranging from it is plain silly to that it is not a useful tool for proper learning.