Move definition of _ and related into Internat.h

src/Internat.h

@@ -16,6 +16,41 @@
 #include <wx/string.h>
 #include <wx/longlong.h>
 
+#ifndef IN_RC
+
+class wxString;
+
+extern const wxString& GetCustomTranslation(const wxString& str1 );
+extern const wxString& GetCustomSubstitution(const wxString& str1 );
+
+// Marks string for substitution only.
+#define _TS( s ) GetCustomSubstitution( s )
+
+// Marks strings for extraction only...must use wxGetTranslation() to translate.
+#define XO(s)  wxT(s)
+
+#define _(s) GetCustomTranslation((s))
+
+// The two string arugments will go to the .pot file, as
+// msgid sing
+// msgid_plural plural
+//
+// (You must use plain string literals.  Do not use _() or wxT() or L prefix,
+//  which (intentionally) will fail to compile.  The macro inserts wxT).
+//
+// Note too:  it seems an i18n-hint comment is not extracted if it precedes
+// wxPLURAL directly.  A workaround:  after the comment, insert a line
+// _("dummyStringXXXX");
+// where for XXXX subsitute something making this dummy string unique in the
+// program.  Then check in your generated audacity.pot that the dummy is
+// immediately before the singular/plural entry.
+//
+// Your i18n-comment should therefore say something like,
+// "In the string after this one, ..."
+#define wxPLURAL(sing, plur, n)  wxGetTranslation( wxT(sing), wxT(plur), n)
+
+#endif
+
 class Internat
 {
 public: