[core] Fix for Get/SetThreadUILanguage() not being available on XP

* This addresses the issue reported in #274:
  Unable to access kernel32 DLL: [0x0000007F] The specified procedure could not be found.
* Problem was introduced in 897becd29015e384754a9fa7728cb4ad14a11cb2 which was added for #189.
v1.4.3 (build 385)