One language technique that Chopin uses is imagry. This is where you use the 5 senses to describe a scene, helping it to seem more vibrant and alive. After Louise has heard the news of her husband's death, she retreats to her room out looks out the window. Chopin describes the scene out her window:
"the tops of trees...were all aquiver with the new spring life. The delicious breath of rain was in the air. In the street below a peddler was crying his wares. The notes of a distant song which some one was singing reached her faintly, and countless sparrows were twittering in the eaves. There were patches of blue sky showing here and there through the clouds"
In this passage, we get the sights, sounds, and beauty that Louise encountered through her window. Chopin uses this imagery to symbolize Louise's coming feeling of freedom. It is a nice day, "new life" was in the air, a distant song was coming to her...all of this symbolizes the "new life" she would be excited to live, free from the constraints of marriage. It adds to the effect of Louise's rather unexpected happiness at the news of her husband's death. So, imagery is one language tool Chopin uses to enhance the mood and foreshadow the elation of the story.
Along those same lines, foreshadowing and symbolism can be considered techniques in and of themselves, so mentioning that fits also, and serves to increase the suspense. She uses irony, which is the opposite of what one would expect, in Louise's reaction, the summarized reason for her death, and in her husband walking in the door at the end. This adds tension, shock, surprise and interest to the story. Chopin also uses a third-person omniscent narrator, a narrator that knows and understands the thoughts of the characters, which helps us to get inside Louise's head, and to know key facts about the story and her heart condition adding to the overall tension and suspense also.
I hope that those thoughts help; good luck!