Many words in Japanese are borrowed from other languages. Many from Chinese, and quite a few from English and Portuguese. A smattering from other languages as well.
The interesting thing about Japanese, though, as opposed to many other languages, is that the Japanese language doesn’t have the syllabic structure to migrate the loanwords over untouched. So when they migrate a word into their language, even though it’s somewhat recognizable as the word they borrowed, it’s not the same word anymore.
For example, “Starbucks”. In Japanese, it’s “sutaabukkusu”, or スターブックス. For obvious reason, a native speaker would never recognize that as a loan word, and even when it’s spoken, it’s not the easiest thing to recognize it unless it’s spoken very quickly. This works the other way around, too: I saw an episode of “AKBingo” where a girl said “You can find me on instagram and twitter”, and the rest of the girls (who did not speak English past what they learned in school) did not understand the words “instagram” or “twitter”, even though those are loan words in their language.
I think one of the difficult things about learning Japanese is getting past the mindset that loanwords, in Japanese as opposed to most other languages, have stopped being words from the origin language, and are, in actually, completely Japanese words. Which is also indicated by the fact that they’re written in katakana.
As I mentioned before, the Japanese never assimilate. They adapt things into their language and culture, but in the process, they always turn those things into something specifically Japanese. Loanwords are another example of this phenomenon. Because arguably, if this was not the case, they would keep those words in roman characters.
There are not many Japanese words in American culture – I can think of only a handful. While we do not use the Japanese character set for them, there are several possible reasons for this. The first is that the English syllabic structure is lossless when it comes to Japanese – unlike the fact that converting from other languages to Japanese changes the phonetic structure of the word, this is not the case the other way around. For words like “tsunami”, “shiitake”, etc., we have more than enough information in the transliteration of the words to keep the pronunciation. Unlike the Japanese language, which does not contain enough information in its syllabic structure to keep the pronunciation of the foreign word.
Culturally, too, we tend to keep the “gairaigo” character of the Japanese word when we import it. There are very few words that we have imported into English that do not either offer some homage to Japanese culture, or that describe a concept that we do not have in English. So there is no reason for us, for the most part, to migrate Japanese loanwords into our language – it is already rich enough. For whatever reason, theirs does not seem to be, at least partially. Even for words like “taifu”, which we misspelled as “typhoon”, we have our own word for that, “hurricane”, so other than as an oddity, we have no reason to import that word.
There is a different kind of loanword, though. This like of loanword exists because the people who import the word find the other language “cool” and import the word simply because they can. Many words in Japanese fit this qualification, and a few in English do as well. “Kawaii” is one example, and “nani” is slowly gaining popularity in the same way. This kind of loanword is a cultural homage, and is never necessary for describing a particular concept that already exists in a language. It’s mostly there just because we think using the words is “cool”.
I personally consider that kind of thing to be too “otaku” for my tastes, to be honest. Use the language or don’t.
Anyway, loanwords are a very interesting aspect of Japanese culture, and seeing how they are used grants an insight into how the Japanese see other cultures and languages. Hint: they take what’s useful and make it Japanese.
This is probably, in my opinion, the most important aspect of Japanese culture for any language learner. It’s not English anymore, even if that’s where the word came from.