This is a good question. Sometimes it is hard determining the meaning of a sentence.
What the sentence is saying is that on certain days he or she is angry (hostile and intricate) and he or she has to hold back from saying things that can hurt people (the bitterness of langauge).
In terms of language, there are a few things to note.
First, there is use of simile. The mind is likened to a place. This begs the question: what kind of place? The place described here is a place that is hostile and intricate and this place holds back the fluid bitterness of language. From this perspective, the sentence is quite poetic.
Second, there is also the use of synecdoche, which means a part represents a whole. Here the mind represents the totality of a person.