Hmm… if you are suggesting what I think you are suggesting, perhaps “jouissance” might be appropriate 
Yep. It is one of the most common errors that Swedes make when speaking English. Amusingly, “rolig” in Danish means calm/quiet.
I think part of the issue is that fun us both an adjective and a noun. “It was fun” versus “I had a fun time”. Many languages have defined forms for their adjectives and as such don’t have a word that can be used in so many ways.
But anyway, in general, when someone says “<word> is unique to <language>” they are generally wrong, as this entry to the Swedish Problems meme puts it:
What’s the grammatically correct version? I’m aware that my Japanese is just slightly awkward, but people aren’t very willing to go grammar nazi verbally, so I’ve never gotten “fixed”.
I’d understand, “Anata wa omoshiroi”, to mean “You’re interesting/funny” rather than “fun”.
Also, one has to be careful about extrapolating from a language to the world view of its speakers, although it’s always a tempting thing to do.
Even if “fun” didn’t easily translate to other languages (which we’ve seen that it does, so it’s moot, but whatever), you can’t necessarily use that to support an argument that English speakers have some unique emotion or experience of fun. I recently started a thread bitching about how the English word “enjoy” can be difficult to translate to Norwegian. We need a bunch of different expression to cover the lexical space of “enjoy”, depending on the context. That doesn’t mean that we Norwegians don’t enjoy ourselves, or don’t grasp the concept. We do. We just say things differently.
You certainly can’t claim that “fun” being both a noun and an adjective in English, while you might need different forms of a word, or different words, for the noun and the adjective in other languages, has some kind of deep cultural significance. That’s extrapolating way too much from a tiny linguistic blip.
You’re missing ‘na’. Tanoshisou na hito.
The Arabic word كَيْفَ *kayfa asks the question “how?”. Used for asking “How are you doing?” (Kayfa ḥāluk?, literally how is your state or condition). From that is derived the noun كَيْفٌ kayf (in North African dialect kīf), which in colloquial Arabic has come to mean a pleasant, gently euphoric state of well-being and feeling at ease and enjoying oneself. Unsurprisingly, the same word is a synonym for marijuana.
The same root also gave rise to كَيْفِيّة *kayfīyah *‘the way how you do something’ and the verb كَيَّقِ *kayyafa *‘to condition’ (air), تِكْيِيفٌ takyīf ‘air conditioning’, مُكَيِّفٌ *mukayyif *‘air conditioner’. The feeling of comfort, like in the noun *kayf *, is common to both meanings.
*hence “Keef Richards”
hibernicus got it. You’re missing the adjective connector, “na”. I understand about how Japanese wouldn’t correct your grammar. They’re happy you can say “konnichiwa”. Some are still amazed that Westerners can use chopsticks ;)
It can mean both, depending on what precipitated that comment. If you told a funny story and someone said, “Anata wa omoshiroi”, it would mean, “You’re funny”. If it was said not as a comment after some certain action, but rather as a general statement, it would mean, “You’re fun/interesting”.
In Italian, fun is *divertimento *(which the musically inclined among you may recognize as a musical form). Divertimento comes from the Latin prefix di(s)- meaning ‘apart’, and the Latin root vert- meaning ‘turn’. Literally something that turns off your mundane cares and replaces it with enjoyment. Like taking a break from your usual cares. I think “divertimento” denotes the referent adequately, though perhaps looking from another angle.
English *fun *may derive from a Norse word for ‘fool, simpleton’, i.e. ‘buoyant, high-flying person’, derived from fáni ‘flag’, which in turn derives from a Germanic root meaning ‘piece of cloth’. Or it may mean girl. That’s right, fun=girl. All I can do is quote Wiktionary’s remarkable etymology:
Alternative etymology connects Middle English fonne to Old Frisian fonna, fone, fomne, variant forms of Old Frisian fāmne, fēmne (“young woman, virgin”), from Proto-Germanic *faimnijǭ (“maiden”), from Proto-Indo-European *peymen- (“girl”), *poymen- (“breast milk”). If so, then cognate with Old English fǣmne (“maid, virgin, damsel, bride”), West Frisian famke (“girl”), Eastern Frisian fone, fon (“woman, maid, servant," also "weakling, simpleton”).
At first I was wondering how “Girls just want to have fun derived from them” might scan to the melody, but then I saw it’s the Eastern Frisians who transfer a chain of meanings from ‘girl’ to ‘weakling’ to ‘simpleton, fool’ to ‘indulgence in enjoyment’. [sigh] Like so much else in histories, language and otherwise, you keep dredging up common everyday stuff that historically originates from misogyny.
Incidentally, the adjective fond also derives from the same Middle English word for fool, fonne.
So which is it? Buoyant, high flying person? Or girl? Who’s the fool? Girl ain’t no fool, uh-uh.
Bengali has [kʰæla] for “play” and [mɔd͡ʒa] and [anond̯o] for “fun.” There are probably several other terms for both, each with various shades of meaning.
I wasn’t. Maybe I wasn’t clear, I was using that as an example as to why some people might think that it is different, not as an argument that it is different.
Clearly they didn’t learn how to have fun until after the languages had diverged! 
No, I’m sorry, I wasn’t picking on you. Just tossing the point out there.
Actually, just to make myself more clear (something I’m not always to good at :p): I was agreeing with you, and expanding on your point.
You know what? It’s essentially an idiom, and whoever wrote that older book was just one of many who have pulled some idiom out and made silly, grandiose generalizations while demonstrating a willful ignorance of the very nature of idioms. Generally the claim is that “no other language has X, the way English/Spanish/Japanese has X,” etc. They go about some simplistically literal lexical translation, and then act as if the fact that no other language has the exact same idiom it therefore means all other language lack the connotation of that idiom. It’s an almost willful ignorance of the way language works.
In Korean, 잼이 있다 seems to be a very good equivalent of “fun”: http://www.korean-flashcards.com/translate-2711
Okee dokee. 