Tin includes a function which checks whether the characters on the system
used in an article can be displayed in the environment Tin is used in:
"locales". Locales are configuration files containing information about
national or regional special features, among other things the language, the
format of numerical data (e.g. if a dot or a comma is used as a decimal
point), the format of time and date or the character set in use. Whenever
the locales are incomplete or misconfigured, all non-7-bit-chars (e.g.
umlauts) are treated as not displayable and a question mark is output as a
substitute.

The configuration which locale adjustments should be used, is made by
environment variables. To obtain full representation of the 8-bit-chars, one
should set LC_CTYPE or LANG to the desired language (i.e. en_US to recognice
all printable chars out of iso-8859-1). If this does not lead to success,
probably the Locale files are incomplete or not installed at all. In this
case you have the possibility (apart from installing up to date locales) to
use a "brute force"-method of compilling Tin from the source using the
option "--disable-locale". After this, the locales will be ignored
completely and any character treated as displayable.