What are five cultural differences in the book Picture Bride?

Cultural differences in Picture Bride by Yoshiko Uchida serve to illustrate the strangeness and sense of isolation that Hana Omiya feels as she adjusts to life in the United States, marriage to Taro Takeda, and life as a mother. They include a difference of language, social structure, beliefs, food, and clothing, each of which serves to separate Hana from others in America and in her own life.
The largest cultural difference and possibly the one that presents the largest barrier to Hana in America is language. She doesn't have a strong command of English and loses her ability to speak clearly when she's troubled or upset. People dismiss her as unintelligent or uninformed when they realize she can't speak English fluently at all times.
Hana recognizes that the language barrier creates an inability to express herself. When she's waiting for a guest one day, she reflects on this. Uchida writes:

She wondered what she could serve Mrs. Johnson. At the same time she tried to put together in her mind the proper words to tell Mrs. Johnson how welcome she was. If only she could tell her what she was just been through, Hana thought, but there weren't enough English words in her weary head even to begin. Hana simply wiped her face with a handkerchief and hurried out to entertain her first white woman caller. (80).

Mrs. Johnson herself embodies this cultural difference in the way she speaks to Hana. Uchida writes that Mrs. Johnson "spoke slowly and raised her voice, as though Hana might be deaf or stupid or both" (80). Because of the language barrier, Hana is assumed to be less adult or comprehending than other American women by Mrs. Johnson.
Language also plays a factor in the wedge between Hana and her daughter later in the novel. Hana thinks that she "had never insisted Mary go to Japanese Language School as some of the Nisei children had done, and she herself had not progressed far in studying English. Now Mary spoke as an adult, while Hana was still a child in the English language" (135). Cultural differences from language to clothing to traditions drive the two women apart for most of Mary's life. 
Another cultural difference is shown in Hana's encounter with Mrs. Johnson; Hana still understands and defines herself by her Japanese beliefs and traditions. Her father is an honored samurai. When people look at Hana, though, they only see a Japanese person at a time when anti-Japanese sentiments in the United States were very high. Uchida writes:

"I suppose you don't do any day work yourself, do you, my dear?" she asked.
So that was why she had come to call. Hana stood tall and looked Mrs. Johnson straight in the eye.
"No, madam, I do not," she answered fiercely. "I am the daughter of a samurai." She would never work for a woman who looked upon her only as a maid.
Hana thus managed to preserve her pride, but Mrs. Johnson left uncomprehending and puzzled, for she had never heard of a samurai and had no idea what Hana meant by her remark, nor why she had seemed so offended. (80)

The difference between the two cultures creates a bridge that makes it difficult for people like Mrs. Johnson to see Hana clearly or to respect her as an equal. She has no interest in knowing why Hana is upset at the implication that she could work as Mrs. Johnson's maid, despite them living in the same neighborhood. She also doesn't stay to find out what a samurai is or who Hana is as an individual—even though she's willing to talk about herself, her family, and her life for the entire visit before suggesting Hana work for her.
Another cultural difference is Hana's belief in the traditions of her childhood. When men come to visit her husband and make it clear the Takedas aren't welcome in the neighborhood because of their Japanese heritage, Hana sets up a broom so that it rests on its handle with a cloth covering the bristles. Taro asks why, and Uchida writes:

Hana's laughter was tinged with embarrassment. "The maid used to tell me when I was a child that setting up a broom like that would send an unwanted caller home quickly."
"Hana, you are still a child," Taro laughed, brushing a light kiss on her cheek.
"I'll do it again when the others come," Hana answered, wondering how long it would be before they appeared. (67)

Taro, who is more assimilated into American culture than Hana, doesn't understand her reliance on old traditions. He sees it as childlike, while Hana is willing to set up the broom again—thus relying on old traditions—when the men come back. She's uninterested in fully letting go of the past that informs who she is in the present.
Food represents another cultural difference in the novel. Hana is mystified that a family like the Davis family chooses to eat what Hana sees as bland food when they have more than enough money to do otherwise. One morning she wakes up and starts making sushi for her husband, Kenji, and the minister. Uchida writes:

She thought of Mr. and Mrs. Davis, in their beautiful house, surrounded by all those posessions that bespoke of wealth. Still, they existed on such dull fare as bread and potatoes, meat and cheese. She wondered if they had ever tasted the countless Japanese delicacies that existed outside their own world. There wasn't one bottle of soy sauce or a container of bean paste in Mrs. Davis's sterile white kitchen. What would Mrs. Davis say, Hana wondered, if she could taste a plateful of her sushi, heaped like a small mountain and garnished with strips of seaweed, sweetened egg and ginger. (86)

This comes after, in Chapter 12, Hana is the object of scorn for having Japanese food with a strong scent that displeases a fellow rider on the bus. She still loves and appreciates the food of Japan but recognizes that not only do other people not know it, they're actively hostile about it. Food is more than just nourishment—it also represents a very large part of the social interaction between people. Hana's experience on the bus and her thoughts about sushi and the Davis family show how ingrained this cultural difference is and the barrier it creates for Hana.
Another cultural difference in the novel is the difference between the clothing of America and Japan. Near the beginning, Hana is already aware that her clothes mark her as an outsider in America. Uchida says:

Hana folded her hands carefully on her lap and looked around, more and more aware of her conspicuous Japanese clothing. "My clothes are not right," she murmured, tucking her feet with their white tabi and zori as far beneath the bench as she could. She held her furoshiki bundle close to her chest, but there was no hiding it or her clothes, and the curious stares of the people who sat opposite her were cold and unfriendly. 
"I feel very much out of place," she whispered. (8)

Without saying a word, Hana's clothes create a barrier between her and other people in American society. A furoshiki bundle is a traditional Japanese square cloth that is used to hold things from babies to food. Tabi are socks designed to be worn with sandals, and zori are sandals that are often worn with kimonos. Wearing traditional Japanese clothing and carrying a Japanese-style bundle in her arms marks Hana as different.
Later in the novel, Hana wears a kimono to feel more connected to her heritage. Though she "was trying hard to adapt to her new country, today she wanted to cling to the familiarity of her kimono, which still felt more comfortable than her western dresses" (41). This shows that no matter how much Hana tries to connect to American society, it never feels as right to her as her own culture.
When she later sees girls dressed in kimonos, obi, and zori at her daughter's school, she thinks that "although wrapped in silken grace, their unaccustomed bodies resisted, and at least in Hana's eyes, they did not look like anything other than foreigners in Japanese dress" (134). It's not easy to integrate into a new culture, even if you change into the garments that represent it. At this point, Hana also reflects on the fact that her daughter is growing away from her and her own Japanese heritage. 
The cultural differences and resulting isolation in Picture Bride weigh on Hana as she tries to stay close to her daughter, Mary. Mary rejects her Japanese heritage and elopes with a white man, then rejects attempts from her mother to reconnect. The novel ends with Hana and Taro in an internment camp after the Japanese strike on Pearl Harbor. Taro is killed by a guard for wandering too close to the barbed wire fence. Hana chooses to stay in the camp and bury her husband rather than return to Salt Lake City to live with Mary and her husband, Joe.