"할인" refers to a wide variety of discounts: it may have a few conditions (minimum quantity, membership, etc.), be available only for a certain period of time, or be a fixed amount or percentage.
"세일" is pretty much the same, although it puts a tiny bit more focus on being a limited-time offer and being percentage-based.
"DC" almost always refers only to a simple, percentage-based discount or rounding down the price. It also sounds much more spontaneous and less formal.
Not mention the infamous "hejter" but so far I don't think there's any good Polish equivalent and people are fine with that loanword - especially politicians.
Any chance the English loanwords stick out to you and the Chinese ones don't because you can recognize English words but not Chinese words?
I can recognize many Sino-Korean words and zero Korean words, so I tend to think of the Sino-Korean words as sticking out.
English/German loanwords just stick out due to there being fewer of them, and they look atrocious in Hangeul, like little dirt islands in a sea of pure Korean and Sino-Korean words.
Since I study Hanja I imagine Sino-Korean words stick out a bit more for me, but I think anyone who's studied Korean for a while can get a sense of the two major groups. They just sound very different.
This is tangential to the topic at hand, but as a Korean learner of ~9 years, it's maddening just how many English loanwords there are. In addition to pure Korean words, there's a surfeit of Sino-Korean (Chinese-derived), or Hanja words. Both of these are beautiful, and then the English loanwords stick out like a sore thumb.
It's trendy to do so, but I think displacing Korean/Sino-Korean vocabulary at this pace is reckless. I think of it as 사대주의 (toadyism) to some degree as well.
---
Some years ago, I went to some cafe and ordered a coffee, like I've done thousands of times here. The employee asked me if I wanted a '디씨' (di-ssi). I had no idea what that was, so I had to ask, and lo and behold: it was shorthand for discount. Discount would be 5 syllables in Korean (디스카운트), an unbelievably long word in a language where most words are 2 syllables.
I was, and am, baffled because Korean already has a serviceable and widely used word that means discount: 할인 (hal-een), which is Sino-Korean (Hanja: 割引). I figure this is some marketing thing, but the same point applies. There are many cases where there's a perfectly capable word that, for seemingly no reason, gets switched out for an English loanword.
Maybe it's to give headaches to anyone trying to learn the language.