16. A text compression apparatus comprising: a number substitution compression unit for assigning a number for a word of local high frequency in text at a first occurrence, and substituting the word with an introduction symbol which is a character string not present in said text, wherein the introduction symbol is with said assigned number at subsequent occurrences for coding, and a number substitution expansion unit for expanding data compressed by the number substitution compression unit by re-substituting the corresponding word for the introduction symbol and number to restore the compressed data to original text.
16. A text compression apparatus comprising: a number substitution compression unit for assigning a number for a word of local high frequency in text at a first occurrence, and substituting the word with an introduction symbol which is a character string not present in said text, wherein the introduction symbol is with said assigned number at subsequent occurrences for coding, and a number substitution expansion unit for expanding data compressed by the number substitution compression unit by re-substituting the corresponding word for the introduction symbol and number to restore the compressed data to original text. 18. The text compression apparatus according to claim 16, wherein said text includes dictionary text having an explanation in a first language applied to a word and phrase in the first language.