Japanese to English
Japanese has possibly the most difficult writing system in the world. Hiragana, katakana and kanji are mixed together, along with the English alphabet, to create written Japanese. Subjects are often omitted, leaving computers unable to produce an English sentence with the requisite subject, and vocabulary items are often shaded with subtle nuance that have to be weighed carefully.
English to Japanese
Many decisions must be made when translating from English to Japanese that a computer cannot compute. Should the verb have a polite ending, such as for a corporate webpage, or a normal ending, such as for a patent? If two people are talking, how should their relative social statuses be reflect in honorific and humble expressions in their speech? Because English does have such features, the translator must use extensive cultural knowledge to produce a natural-sounding Japanese text.
English to Chinese
Unrelated to Japanese, Chinese is in fact more similar to English at least in structure as they both have SVO (subject-verb-object) style sentences. An important decision to make for translating to Chinese is the target locale. Although mainland China, Hong Kong, Singapore and Taiwan all use Chinese characters, there are significant differences in vocabulary, and the simplified and traditional scripts are very different in appearance, even though they are generally mutually undestandable.