Yeah, the tags are entirely up to the posters. That's one of the self-organizing aspects of the network that takes a deal of time to work itself out. Sadly, there aren't any good ways of filtering these on the steemit web site, so either you end up with all of the noise, or just the noise that makes it into trending.

I'm going to start including the #languagelearning tag in my related posts, but I don't know if I will bother with the #steemstem one.

It seems I've also become an infrequent poster. Life keeps getting in the way of me being "social" ;-)