“I have tried learning a language before (Danish) before, but got only so far then stopped. Everytime I pick it up again, I start from the beginning. This has allowed me to develop a very sound understanding of some basic sentences. Will this eventually happen for the entire language?”
You probably don’t actually start from the beginning, it just feels like that since you have forgotten quite a bit. But likely, you do remember some things and some things will come back more easily.
Chinese is the language that I speak at the lowest level, so it’s probably most similar to your Danish.
Basically, I started learning words and phrases and I would recognize things here and there. As I worked on it consistently, I would understand more and more. I would be able to understand the meaning of simple statements. But there would often be words that I did not understand.
Sometimes that would make me want to learn those words, unless they were very uncommon.
With Spanish, I probably understand about 95% of what I hear. So I understand most things. And I do try to keep learning more words.
In between Chinese and Spanish is German for me. I understand quite a bit, but my level has decreased substantially in the years it has been since I was in Germany.
Much better not to stop practicing completely if possible!