Bleak House is acutely concerned with questions of when to speak and when to remain silent. Part of Esther's maturation is understanding how and when to deploy criticism: keeping quiet maintains social bonds, while offering judgment can sometimes repair a wrong. However, the choice to speak is riddled with its own secondary decisions about manner and medium. Sir Dedlock's highly formal affirmations of love sound too trite for Lady Dedlock to put stock in his forgiveness, while Jarndyce's proposal by letter rather than voice places a distance between the passion on the page and his calm manner in person.
The ability to modulate language to a specific audience is a skill only developed by those who serve or wait on others. The powerful have no need to differentiate the people they are addressing.
Written communications in the novel are far more important as physical objects than for whatever their content might be. The love letters found with Hawdon's body, for instance, are never read, but their existence as a little packet tied with red ribbon is crucial. It's the same with the documents in the Jarndyce case, which are too numerous to fit into the bags they're carried in. Because of this, non-language-based modes of communication, like Woodcourt's bouquet, take on infinitely greater meaning than they would otherwise.