I'm searching for a document (not printed) that explains in details but still simply the subject of character encoding.
Wikipedia is actually as good a source as any to begin with:- http://en.wikipedia.org/wiki/Character_encoding>Character-Encodings. As well as the more familiar ASCII, UTF-8 etc. they have good information on older schemes like fieldata and the various incarnations of EBCDIC.
For in depth info on utf-8 and unicode you cannot do any better than:- http://www.unicode.org>Unicode.org
Various manufacturs sites such as Microsoft and IBM have lots of code page info but it tends to relate to thier own hardware/software products.
See section 2 onwards of this document http://ahds.ac.uk/creating/guides/linguistic-corpora/chapter4.htm, it has an interesting history of character encoding methods.
A great overview from the Programmer's perspective is:
The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)
By Joel Spolsky
There is a French book about this called Fontes et codages by Yannis Haralambous, an O'Reilly book, I'm pretty sure it is or will be translated. Indeed, it is: Fonts and Encodings.
A short explanation of the basic concepts: http://www.mihai-nita.net/article.php?artID=20060806a