Replace a ton of trivial #ifdefs with runtime checks

This one is big, but unless I missed something, should be all be
trivial.

scripted-diff with the following, then manually tweaked whatever needed:
```

if [ $# -ne 3 ]; then
    echo "Usage: $0 '<pattern>' '<replacement>' '<filename>'"
    exit 1
fi

pattern="$1"
replacement="$2"
filename="$3"

if [ ! -f "$filename" ]; then
    echo "Error: File $filename does not exist."
    exit 1
fi

sed -i '/'"$pattern"'/ {
    :loop
    $ !{
        N
        /'"$pattern"'.*\n.*#endif/ {
            s/'"$pattern"'/'"$replacement"'/
            s/#else/} else {/
            s/#endif/}/
            P
            D
        }
        /'"$pattern"'/ b loop
    }
}' "$filename"

echo "Replacement complete in $filename"
```

h/t to Grok2 for the sed command

Ja2/Intro.cpp

@@ -36,6 +36,7 @@
 
 #include "LuaInitNPCs.h"
 #include "XML.h"
+#include <language.hpp>
 
 BOOLEAN Style_JA = TRUE;
 extern INT8 Test = 0;
@@ -726,11 +727,11 @@ void DisplaySirtechSplashScreen()
 			*								(2006-10-10, Sergeant_Kolja)
 			*/
 			#ifdef _DEBUG
-			#	if defined(ENGLISH)
+			if( g_lang == i18n::Lang::en ) {
 				AssertMsg( 0, String( "Wheter English nor German works. May be You built English - but have only German or other foreign Disk?" ) );
-			#	elif defined(GERMAN)
+			} else if( g_lang == i18n::Lang::de ) {
 				AssertMsg( 0, String( "Weder Englisch noch Deutsch geht. Deutsche Version kompiliert und mit englischer CDs gestartet? Das geht nicht!" ) );
-			#	endif
+			}
 			#endif
 			AssertMsg( 0, String( "Failed to load %s", VObjectDesc.ImageFile ) );
 			return;