Most of what are generally considered languages, whether natural or constructed, are in fact two languages, one written and one spoken. We usually learn the two together, and thus learn the mapping between them. These can vary in how obvious they are. At one extreme are languages that use a very standard mapping. It is virtually impossible to be able to read the Roman alphabet - in English or French, say, and to be able to speak Portuguese, but not to be able to read Portuguese, as a friend of mine found out. She had these skills but had never learnt to read Portuguese. Her mum was shocked to find her reading a book in Portuguese and asked where she learnt to do that. She had not learnt - she could just do it.
The next step is English or Gaelic (and not many other languages) where the mapping is so poor that it is possible to be fluent in the spoken language, and not to be able to read the language, even though you can read another language in the same alphabet. 100 years ago there was a famous disaster involving a ship called the Iolaire. Virtually everyone on board, and the bereaved relatives, had Gaelic as a first language, but they could not read Gaelic and so had no idea the ship's name was Gaelic - they pronounced it as an English person would and had no idea what the name meant.
Next come languages like Chinese, which is in fact several spoken languages, with one written language. The symbol 米 means rice. How you pronounce it varies according to whether you speak Mandarin or Cantonese, or even Japanese which sometimes uses Chinese symbols (Kanji). Thus you can learn written Mandarin (you now know one word) with no clue as to how to pronounce it.
We use some logograms in English. Some, such as ☏, are pictographic in origin, and so have no inherent pronunciation - we just translate them to English as we read them. Others, such as &, are alphabetic in origin. This one is a fancy way to write et, which is Latin or French for "and". We ignore this and just pronounce it "and". Of course other people, such as the Germans, will pronounce these symbols differently.
You could always learn a natural or constructed language from a book that had no pronunciation guide, if it was written in Cyrillic, using Chinese characters, or using its own made-up logograms. But of course, you could find out how to pronounce it.
Next, a language could be constructed without a vocal form. I am not aware that this has occurred. The problem here is that there is no way stop someone inventing a vocal form for each symbol. This is a bit like learning Old English or Ancient Greek. We do not know exactly how they were pronounced, and so we use what is basically a modern guess.
The only examples I can think of where there is no vocal form is the sign languages used by deaf communities. They are genuine languages, unlike signed English, and usually have no accepted spoken or written form.
