- remove use of boost in src/Main/locale.cxx;
- add missing header <cstring> for std::strlen();
- replace NULL with nullptr;
- fix some broken indentation;
- other small readability improvements.
This function returns the preferred "locale"[1] according to user choice
and/or settings (i.e., it is influenced by --language if passed,
otherwise by current locale/system settings). The return value never has
an encoding part. It is the empty string if nothing could be found,
otherwise should look like fr_BE or it_IT.
[1] "language" term used in the function name for consistency with the
existing and related FGLocale::selectLanguage().
Windows and Mac implementations return a string without any encoding
specifier -> remove this specifier directly in the Unix/Linux
implementation for consistency.
Also do some small refactoring with the new static method
FGLocale::removeEncodingPart(). Slight difference with the previous
algorithm: if a '.' is found in the given locale spec, we assert() that
it is not the first character. The previous code in
FGLocale::findLocaleNode() used to consider such weird locale specs
starting with a dot as normal locale specs without any encoding part.
Note: the same change could be done where FGLocale::findLocaleNode()
looks for an underscore in order to prepare for the fallback
search (e.g., 'fr' after not finding translations for 'fr_FR').
Respect the user's language selection in the system settings, and try those languages in turn. If a language is explicitly specified, try that first regardless.
