No, I am a follower of Wittgenstein’s notion of “language games” where all language is socially constructed by groups of people participating in a self-perpetuating linguistic context. It is an objective phenomenon as words which have no meaning to another person cannot exist.

The Treachery of Images by René Margritte

The text in the painting reads “Ceci n’est pas une pipe” which (more or less) translates to “This is not a pipe.” What Margritte is saying is that literally it is not a pipe, it is a painting of a pipe. But it’s also not just a painting of a pipe, it is an image of what Margritte holds as his internal concept of a pipe.

Communicating complex ideas to others is difficult because words hold different meanings for different people and the more nuanced the more language starts to get in the way. But all communication is imperfect.

It’s not solipsistic though because much of the meaning you might hold for words is contextual to the people who taught you language and your relationships with others. Your conception of those word’s meanings are your interpretation of the meaning someone else holds. Language and communication are much more effective viewed from the perspective of collaboration rather than expression. In other words working to establish shared understanding makes communication more effective.

They aren’t different sources of info, but parts of the same process. And they’re three:

1. The utterance. Like you said, the words and how they’re arranged and such.
2. Your internalised knowledge. It’s all that bundle of meanings that you associate with each word, plus your ability to parse how those words are arranged.
3. The context. It’s what dictates how you’re going to use your internalised knowledge to interpret the utterance; for example, selecting one among many possible meanings.

Without any of those three things, you get 0% of the info. They’re all essential.

So no, it is not solipsistic at all, since it depends on things outside your head (the utterance and the context), and those are shared by multiple individuals.

Language arises out of social behavior, beginning with imitation and reinforcement in early childhood. Children who don’t learn language (by interacting with adults and older children) in the critical period of early childhood, suffer serious developmental problems. So language is fundamentally anti-solipsistic, even anti-individualistic: you only acquire it by being brought into a community of language-users.

And written language begins as an encoding for spoken (or signed) language: everyone learns to speak (or sign) before they learn to read, and learning to read starts with learning associations between written structures and spoken ones. (For English-speakers, that means phonics: the relationship between letters or groups of letters, and sounds.)

Meaning isn’t “assigned” solipsistically; rather it’s “acquired” from a community of use. A single user can’t decide for themselves that “dog” means squirrel. I suspect that if you look at the word “dog” and try to convince yourself that it refers to a bushy-tailed tree-climbing nut-munching rodent, you will be aware that you are doing something very silly, something deliberately contrary to your knowledge.