I deliberately chose not to teach my children my or my wife's fairly obscure and mutually completely unintelligible languages.
On the other hand, I ensured that they studied Latin, Italian, French and Sanskrit in addition to their L1 ( English )
I am a polyglot and know around a dozen languages to various levels, including several semi-obscure minority languages.
A lot of culture co-evolves with language. In a language are myths and legends, some of which contribute to the words in the language, which then give birth to other proverbs and stories, and so on. All of which and fragments of which become available for communication. The more knowledge and culture a language loses, the more bland communication in that language becomes and the information density of the language decreases. This in turn affects communication because to maintain the same amount of information it has to become longer, so the attitude towards communication changes. And so does the message.
The tool of communication is part of the message itself.