First of all, discard the notion that Japanese is the most difficult language in the world to learn. The truth is that every language has its quirks and its bonuses. Some areas of difficulty are universal to all languages -- like homophones, for instance -- words that sound the same but have different meanings (rows, rose [flower] and rose [past tense of rise]).
Here are some of the quirks that native speakers of Western languages should be prepared for when learning Japanese:
I. Ideographic, syllabic writing system
II. Use of "particles"
III. Lack of articles, plurals and pronouns
IV. Lack of intonal stress
V. Humble/honorific forms
VI. Gender-specific words
VII. Counters
I. The writing system Japanese as a spoken language is based on syllables, rather than individual letters. As a result, there are a limited number of sounds and sound combinations available from which to form words. This results in a large number of homophones (words which are pronounced the same), which require a special writing system to clarify meaning.
So, the Japanese continue to use the Chinese system of writing called "kanji" for the bulk of their written communication. This, however, is not the only writing system in use by Japanese. It's supplemented by two 46-character syllabic scripts called the "kana." They are hiragana, for the writing of native Japanese words and for showing which suffix to use with a written kanji, and katakana, primarily for the writing of foreign "loan words," other than Chinese, which have crept into common use in Japan. These loan words are usually English, but are sometimes French, Italian, etc.
The thousands of Chinese characters (the kanji) that make up the majority of written Japanese nouns, verbs, adjectives and adverbs come from Chinese ideograms imported from China and Korea, beginning in the 6th century. The Japanese adapted these characters, sometimes using them only for their sounds, and other times retaining their meanings as well.
Because kanji were imported from China, they have both Chinese and Japanese pronunciations, both of which are used commonly in Japanese. The Chinese reading is called the on-yomi, which is the Japanese interpretation of the ancient Chinese pronunciation. The Japanese reading is called the kun-yomi, which is the original Japanese word for the ancient Chinese character.
