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6.6 Where You Are Makes a Difference
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Modern systems support the notion of "locales": a way to tell the system
about the local character set and language.  The ISO C standard defines
a default '"C"' locale, which is an environment that is typical of what
many C programmers are used to.

   Once upon a time, the locale setting used to affect regexp matching,
but this is no longer true (*note Ranges and Locales::).

   Locales can affect record splitting.  For the normal case of 'RS =
"\n"', the locale is largely irrelevant.  For other single-character
record separators, setting 'LC_ALL=C' in the environment will give you
much better performance when reading records.  Otherwise, 'gawk' has to
make several function calls, _per input character_, to find the record
terminator.

   Locales can affect how dates and times are formatted (*note Time
Functions::).  For example, a common way to abbreviate the date
September 4, 2015, in the United States is "9/4/15."  In many countries
in Europe, however, it is abbreviated "4.9.15."  Thus, the '%x'
specification in a '"US"' locale might produce '9/4/15', while in a
'"EUROPE"' locale, it might produce '4.9.15'.

   According to POSIX, string comparison is also affected by locales
(similar to regular expressions).  The details are presented in *note
POSIX String Comparison::.

   Finally, the locale affects the value of the decimal point character
used when 'gawk' parses input data.  This is discussed in detail in
*note Conversion::.