I’ve been conducting an experiment on myself to see whether it’s possible to undo deeply entrenched Chinese pronunciation & tone mistakes I’d accumulated over the years (otherwise known as fossilisation.) I document the results in this blog – I Conducted an Experiment to See if I Could Overcome Chinese Accent Fossilisation. Here are the Results – I'm Learning Mandarin
Ah fossilization. I just read a book on 2nd language acquisition and it talked about that a lot. They used it with respect to grammar mostly. From my experience learning Japanese I think I can still improve my pronunciation even after years of studying Japanese. But at the same time, certain sounds are difficult (which is why I didn’t learn them correctly in the first place). A lot of people make a big deal about if you develop bad habits you’ll never be able to fix them. Well, I have English speaking habits already so I have to unlearn those meaning I’m already screwed from that point of view. I’m not a blank slate - I’m not a child learner.
I think if you put effort into and study a sound to where you can self correct then you’ll naturally improve. Sure, it would be nice if you fixed your pronunciation errors early on but beginners have a lot on their plate as it is.