SDL: Remove side effect of setlocale() call to get Language.

This is to fix bug #3615148 -  "ALL: sscanf("%f"), atof() etc. not
portable due to Locale"

The side effect of setlocale("") is to change the active locale
from the default of "C" to the detected system locale, but this
changes the behaviour of sscanf() and several other functions
in a system dependent and non-portable way. This has caused
bugs in the ZVISION engine when running Zork Nemesis.

The solution is to restore the default "C" locale after the call
to get the language.

Thanks to criezy for working out this fix.