> For example, there are words in dictionary that should not be defined using other words (but dictionary still do, this sort of circular reasoning is something I always have problem with)You shouldn't. When you learn a foreign language dictionaries can be a great help and it doesn't matter if they use circular definitions. Well it can matter in a situation like Stanisław Lem described with his "sepulkas"[1], but even then the definitions were a red warning. Ijon Tichy just failed to understand it.
> you would not be able to do so unless the kid touches something really hot like boiling kettle to "feel" it
I learned English by reading books mostly. In most cases I had no easy access to a dictionary and inferred meanings of words by a context. In some cases I failed to infer meaning but nevertheless in each case I managed to get some idea about a word. I remember some surprises when I found a real meaning of a word and it was not exactly what I thought. Or even some ideas that felt new and inspiring for me before I connected them to ideas I learned long before that in my native language. I'm like an English LLM myself, because I never used English in a real world context, only to read texts and to write comments in English. To this very moment I cannot talk about some topics in Russian, because I do not know Russian words to talk about them.
All this experience led me to doubt an idea that you can understand language only by connecting it to reality. I believe you can. Your language will be disconnected from reality and it can be a disaster probably if you try to apply it to reality, but you can talk a lot, participate in philosophical debates and it doesn't matter your understanding is different. It is like redness of red: do you see red as I do and does it matter?
> There are things we just cannot understand through language.
We cannot link our senses with language without burns. But it doesn't mean we cannot understand. For example, you can watch other people touching really hot boiling kettles. If you never touched anything hot you will not understand their pain, but you'll know they are in a pain and you'll know of a special nature of that pain. You can learn all the important intricacies of interaction with hot objects by just watching. Or by reading. Your understanding will be limited still, but in a lot of cases it doesn't matter.
Though of course we coming very near to a debate what is understanding. Is it a human-centric definition, that boils down to "only a human can understand", or it is more relaxed and rely on a pragmatic idea, like does your understanding enables you to make right choices. If LLM doesn't have a body that can feel pain, it doesn't matter if LLM cannot know how pain feels.
[1] https://en.wikipedia.org/wiki/Sepulka