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*                                                                             *
*                            INTERNATIONALIZATION                             *
*                                                                             *
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* Locales.

  Nail uses the LC_CTYPE locale setting to determine whether a character is
  printable; if it is not, it is replaced by a question mark when writing a
  message to a terminal. On most current systems, LC_CTYPE is an environment
  variable. It has to match the character set of the terminal nail runs on;
  however, the character set can often not directly be determined by just
  looking at the environment setting.

  In case the system's locales are totally broken, all support for locales
  and other internationalization issues can be disabled by supplying a
  "--enable-all-chars" parameter to "configure" when building nail. This
  should only be used as a last resort since it drops useful functionality.

* Character sets.

  Since it is impossible to determine the character set of a given locale
  in a portable manner, nail may need additional information about it. There
  are two nail variables to set in this context: First, "charset" determines
  the character set of outgoing messages. As this parameter is written
  directly into the message's header, its value has to conform to the
  definitions given in RFC 2046. The most commonly used values are currently
  "iso-8859-X", where X is between 1 and 15, or "koi8-r" in Russia etc.

  In most cases, the "charset" value will be the same as the terminal's
  character set. In some situations, however, it may be desirable to
  use different ones here; since Unicode messages are not generally well
  understood by all mail user agents, users of an Unicode terminal may
  choose to send in an ISO 8859 character set. For this purpose, the
  "ttycharset" variable can be set; it defaults to the "charset" variable.
  On systems where the CODESET parameter to nl_langinfo(3) is available
  (e. g. on those conforming to SUSv2), nail determines the terminal's
  character set dependent on the LC_CTYPE locale setting at startup. If
  this call is possible, the result is assigned to "ttycharset".

  When nail is displaying a message out of a mail folder, the character
  set that is indicated in the message's header is tried to convert to
  the terminal character set, using "ttycharset", or, if unset, "charset".

  If the values assigned to "charset" and "ttycharset" (or the automatically
  determined terminal character set) differ, outgoing messages are tried to
  convert, too; the conversion will fail, of course, if a character cannot
  be represented in the new set, and the message will not get sent. It must
  be noted that the error conditions are somewhat vague; thus some testing
  should be done before messages actually get sent to the outside world
  this way.

* Unicode.

  Wherever an useful iconv(3) function is available, nail can send and
  display Unicode messages. Unless the terminal also supports Unicode,
  messages originating from foreign environments will contain mostly
  question marks when viewing, however; this does not affect outgoing
  messages.

  Recent versions of the "xterm" program contain experimental Unicode
  support. When such a terminal is used, the "ttycharset" variable
  can be set to "utf-8", and a vast number of international characters
  are supported at once. It is quite recommended not to send UTF-8
  messages today since most receivers will not be able to read them
  correctly, so the "charset" variable should contain a more common
  character set name like "iso-8859-1" or "koi8-r".

  To make real use of such a terminal, the pager and the editor have
  to support UTF-8, too, as on many recent System V variants. You
  might also try the "pg" command available from my home page at
  <http://omnibus.ruf.uni-freiburg.de/~gritter/> for viewing, and,
  as a last resort, the classic "ed" editor for writing. The latter
  will do this work as long as you do not use regular expressions.

* System dependencies.

  To perform character set conversions, the system's iconv(3) function
  is used; it should be present on all System V Release 4.2 variants as
  well as on recent Linux systems. This function, however, suffers from
  a serious design flaw: the character set strings it accepts are absolutely
  implementation-dependant. Currently, the following implementations are
  tested:

  - GNU C Library 2.1, 2.2.

    This implementation supports many of the character sets that are defined
    in RFC 2046 respective the IANA tables and knows of its names, too. Version
    2.2 includes full UTF-8 support.

  - Solaris 8.

    At least the conversions between Unicode/UTF-8 and the ISO 8859 character
    sets are supported. The use of this implementation is a bit difficult
    since the names it accepts are proprietary and case-dependant. If this
    leads to error messages such as 'Cannot convert from 646 to iso-8859-1'
    you have to specify the terminal character set by hand, as e. g. the
    nail command 'set ttycharset=iso-8859-1' does.

  - UnixWare 7; 2.1.

    This iconv() is nearly useless since not only the character set names
    are proprietary and case-dependent; the conversion directions are
    limited, too.

Gunnar Ritter	9/29/02
