In the movie Blade Runner, the future Los Angeles(2019) is depicted as having lots of chinese people and chinese influence. Why is that the case?
If you look at the demographics when the movie was made, the immigrant Chinese population was growing very quickly. It was quite reasonable to believe that they would attain a significant enough population to have their own sections of town (even large ones) where Chinese culture was not subsumed by American culture, and where Chinese was freely spoken.
In fact, I believe this has happened. Many large cities, especially on the west coast, have large enough populations of first generation oriental immigrants that mainstream businesses have begun accommodating them. For example, in my day job I'm a web developer. One of my company's clients is a funeral home in California. Slightly less than one-quarter of the funerals they hold are held largely in Chinese (and a smaller number in Japanese or Korean), as is much of the data we receive from them (obituaries and so forth).
To expand on Xantec's answer: if I recall, the Chinese sections in Blade Runner's LA were fairly run-down, densely packed with people, and the authorities didn't have much penetration into the areas (as is typical with suburbs with a strong national influence and community sense of belonging). This would make it a good choice for the fleeing Replicants.
In short, it is a bit of realism in the sci-fi setting, and the Replicants are there because of it.
There are several answers, including Ridley Scott thinking big neon kanji (or possibly hànzì, the Chinese ideograms) characters are cool. In fact, I would guess that's a primary reason.
It's been a good long time since I read Do Androids Dream Of Electric Sheep, but I'm very sure that demographic isn't part of PKD's novel. What I do remember is that, by the time the movie starts, everyone who was in good physical condition had gone, leaving a fairly empty city. There's signs that this was part of the movie: Sebastian's Methuselah syndrome, Tyrell's age and really thick glasses, Gaff's pockmarked face. By and large, I'm seeing the same thing with the rest of the population. Chew and the restaurant lady and the "fish scale" are oriental and old. The guy who made the snake is arab and obese. It seems that, instead of generally emptying everything equally, people are flocking to the ruined Los Angeles and getting out of lesser-populated areas. But that only goes so far. Why would anyone live in a wet and rainy L.A. when the forests in the last reel are in driving distance?
Ultimately, the Chinese population of future LA, like the climate change from desert to constantly raining, exists because Ridley Scott thought it would make a good movie. And I believe he was right.
Is it the entire city? I may be wrong but I don't believe we ever see more than a few small parts of the city in the movie. Most likely by coincidence the replicants just chose to hide out in the Chinese quarter.
maybe it is a reflection on some of PK Dick's other books; the Man in the High Castle depicts a future where the Japanese occupy the Western USA after winning WW2. In that book, everyone wears Kimono and western culture is considered to be a dying tradition, inferior to Japanese. Also, what was more modern and futuristic than Hong Kong or Tokyo back in the early 80s?