Hm...I've been wanting to post an introduction to the language for a while....so here we go (this will be LONG):
The Japanese Language *dramatic drum roll*
Contrary to what many people think, the Japanese language isn't actually related to other Asian languages very closely, not even to Chinese. Looking at the grammar, it is actually related to Turkish and Finnish.
There are a couple of special features of the Japanese language.
For one, Japanese does not distinguish between singular and plural. If you want to make it clear how many things you are talking about, there is a suffix you can use after people (f.e. kids, teachers, person) or you have to count.
Which brings us to another point: Counters. Both Japanese and Chinese use counter words. Counter words are suffixes, so they are placed after the number. There are specific counter words for pretty much everything. There is a counter word for flat objects (sheets, stamps, letters), one for minutes, one for hours, one for people, one for small animals, one for electronic devices, one for long cylinders (bottles, pens, trees), etc. In short, you need to know what counter word goes with the thing you are counting. If you don't know which counter to use, there is a universal counter, but it only works up to ten....so for more things, you won't get around learning a counter. The annoying thing is that some numbers will be irregular in combination with a counter....so there's even more to keep in mind.
As an example:
"Hon" is the counter for bottles, but the "h" will change to "p" or "b" in combination with certain numbers (usually 1, 3, 6, 8, 10)
one = ichi + hon -> one bottle = ippon
two = ni + hon -> two bottles = nihon
three = san + hon -> three bottles = sanbon
etc.
Japanese also has neither conjugations nor declinations. So if I use the word "ikimasu" (to go), I can mean "I'm going", "you're going", "we're going", etc. Non-native speakers tend to use a lot of pronouns to make up for this lack of conjugations, so they'll add a lot of "I", "we", etc. Japanese speakers tend to have a good intuition about who is meant, but sometimes you really have no idea if you are supposed to do something or if the other one will do something....because Japanese sentences can just consist of the verb. That makes the language very vague.
As for the declinations.....I'll get to that.
The word order also doesn't matter. The verb always comes last. That's the only rule. Little words, called "particles", mark the relationship between your words. So you don't need declinations for that. There is a particle for the main subject, sub-subject (can't think of a better word), object, a question particle, one for direction..... They aren't as numerous as the counters, so don't worry. You can learn them easily. You always stick them after the word they are referring to.
As an example.....take this sentence.
Ema kills Dally.
You take the particle for the subject (wa) and the particle for the object (written as "wo", but just pronounced as an "o"), and move the verb to the end
So you end up with:
Ema-ha Dally-wo kills.
(You'd probably add "san" to the names, but let's keep it simple for now.)
If Dally kills me:
Dally-ha Ema-wo kills.
Even though the word order doesn't matter, you usually put what you want to emphasize at the beginning of a sentence, so in this case the culprit.
One of the nicest things about Japanese is that it only has a few tenses. You have the present tense (mostly used for expressing things in the future), a progressive tense (for things right now or things that went on for a long time) and only one past tense.
Apart form that you also get a passive (usually used to express bad things that happened to you), a causative (used when you let or make someone do something) and imperative tense for orders (very impolite!). And then there are the te-form and the ta-form, which both have lots of functions....but I won't get into detail here.
A more complex aspect of Japanese is that you have a polite/formal way of talking (like the German "Sie" or the Spanish "usted/ustedes") and an informal one (the German "du" or Spanish "tu"). You have to learn which one to use in which situations. It depends on your social rank and age in relation to the person you are talking to. Sometimes this can be very strict. A colleague, who has been in your company a year longer than you, or an older classmate, is already ranked higher than you and you are expected to speak with him in the formal manner.
Formal and informal style is marked at the end of the sentence. The aforementioned "ikimasu" is formal. We call the formal style "desu/masu" style, because the verbs will end in "masu". "Desu" is the formal form of "to be" and is added after nouns or adjectives (if there isn't any verb at the end of the sentence).
The informal version is called the dictionary form, because that is the one you will find if you look for a translation in the dictionary. In the case of "ikimasu", it is "iku". All informal verbs end in "u", except if it's the negation or the past tense (or the negation of the verb in the past tense). Then you need to know how to form the polite form based on the dictionary form. But there are rules for that.
There is also a super formal version of Japanese. But you will only get to hear that in the service sector. Customers will be addressed that way. It's rather obnoxious, because then you use the passive tense (just to make everything polite) for the verbs (but ignore that for the real passive, you would need to switch the particles of the object and subject). And some verbs have their own versions that will be completely different in this super formal style....which even has two different variations: The one where you are using humble expressions for yourself and the one with which you flatter your conversation partner.
In this super formal style, "ikimasu" turn to "mairimasu" (if you are going, because you are being humble about your own actions) and to "irasshaimasu" (if your conversation partner or someone ranked very high is going). As you can see, it is rather different from the original one, but as a beginner of Japanese, you won't run into that form for a long time, anyway. And you rarely get to hear it as it is.
Now....about
the writing system....
Japanese is written in three different alphabets! Luckily, two of the are so-called "syllable" alphabets. They have a limited number of letters and you can learn those easily. The third one is the Chinese alphabet, which the Japanese started using almost 2000 years ago (they had no own writing system before that; the other two were developed later).
The three alphabets are:
Hiragana: Originally the alphabets women used. Very curvy, and used for a lot of things. Basically, you write the nouns, adjectives and verb stems in Chinese characters and then everything else (like endings of the verb for past tense, particles, etc.) in Hiragana.
Katakana: Used to be the men's alphabet and has sharper lines. It's mainly used nowadays to write foreign words in Japanese or to emphasize something. Also, when Japanese learn a foreign language the pronunciation is often written in Katakana.
Chinese alphabet: Called "Kanji". Officially there are 2000 common kanji. Once you have learned those, you are supposedly able to read the newspaper. If you think that's a lot, for Chinese you need to know at least 10,000. So it could be worse.
To give you an example of what those alphabets look like....here is "Tomorrow I will fly to England":
明日私はイギリスに飛びます。
明日 私 飛 are all kanji. The first two mean "tomorrow" (literally "bright" and "day"), then you get "I" and the last one is "to fly".
は に びます are hiragana. The first one is the particle "wa" for the subject. The next one is the particle for the direction (to England). And the rest is the ending of the verb, in this case formal present tense.
イギリス is England in Katakana. Literally "i gi ri su".
You can learn the first 500 kanji or so relatively easily, at least the meaning. The annoying thing is when they show up in combinations and you know the individual meanings, but not the meaning of that combination (like "tomorrow" in the example). Another issue is the pronunciation of the kanji, because there are usually many different ways to pronounce one kanji, and you need to memorize in which cases to use which pronunciation....I'll try to make this a bit more clear.
If you get a kanji on it's own (not followed by another one), you usually use the Japanese pronunciation. But for kanji composita (several together, like 明日), you usually (but not always!) use the Chinese-Japanese pronunciation of the individual characters. Chinese-Japanese means that back when the Japanese adopted the Chinese alphabet, they had this idea of trying to stick to the Chinese pronunciation as well as they can. But sometimes it didn't work and a long time has passed since then, so in many cases the "Chinese" pronunciation of the kanji is different from the actual pronunciation in Mandarin Chinese.
Sometimes this mixtures of readings can be very annoying, esp when you have three or four "Chinese" readings for one kanji and just don't know which one to use. I'm afraid you just have to memorize it.
So....can you read Chinese if you can read Japanese or vice-versa? Yes and no. Chinese can usually understand half of a written text in Japanese, but the other way round is more complicated, because the Chinese Mainland (not Taiwan) has introduced "Simplified Characters", so basically changed/simplified the way you write many of the Kanji. A lot of Chinese can still read the "traditional Characters", though, so they can understand written Japanese to a degree. They don't know what to do with what's written in the other two alphabets, though (which give you additional, essential information). But Japanese who don't know Chinese may not recognize the simplified version of the kanji they know (some simplified version are close to the original and can be guessed, others are rather different).
If a Chinese speaker looks at my sentence above, he/she might understand "tomorrow" and "fly", but wouldn't know where to or if it's a negation (-> I won't fly tomorrow), because that information is not written in kanji. Also, the Japanese kanji for "I" has a different meaning in Chinese, so that would also confuse him/her. Usually kanji have the same meaning in Japanese and Chinese, but not always. So there are traps.
In terms of pronunciation, the two languages are also vastly different. If you listen to them for a longer period of time, you will notice that they don't sound alike at all. Korean and Japanese sound somewhat similar, though, to the point that sometimes I'm despairing because I can't understand anything, only to realize later that it's Korean....
Long story short: Chinese, Korean and Japanese are rather different from each other.
I think that's it for now. If I remember something, I'll post it later.
Despite the rules, certain things you cannot do in the UK are fine there...like in parks you will see signs that say "Be gentle with the grass" as opposed to "KEEP OFF THE GRASS". So in the spring you will see groups of students setting up barbeques under the cherry blossom, having some cooked food and some beers and a nice chat, it's called HANAMI (flower, see = direct translation)...try that in Kensington Gardens! 
