patch 8.0.0094
Problem:    When vimrun.exe is not found the error message is not properly
            encoded.
Solution:   Use utf-16 and MessageBoxW(). (Ken Takata)
diff --git a/src/os_win32.c b/src/os_win32.c
index f8e0f11..34b2ca8 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -4705,12 +4705,24 @@
 #if defined(FEAT_GUI_W32)
 		if (need_vimrun_warning)
 		{
-		    MessageBox(NULL,
-			    _("VIMRUN.EXE not found in your $PATH.\n"
-				"External commands will not pause after completion.\n"
-				"See  :help win32-vimrun  for more information."),
-			    _("Vim Warning"),
-			    MB_ICONWARNING);
+		    char *msg = _("VIMRUN.EXE not found in your $PATH.\n"
+			"External commands will not pause after completion.\n"
+			"See  :help win32-vimrun  for more information.");
+		    char *title = _("Vim Warning");
+# ifdef FEAT_MBYTE
+		    if (enc_codepage >= 0 && (int)GetACP() != enc_codepage)
+		    {
+			WCHAR *wmsg = enc_to_utf16((char_u *)msg, NULL);
+			WCHAR *wtitle = enc_to_utf16((char_u *)title, NULL);
+
+			if (wmsg != NULL && wtitle != NULL)
+			    MessageBoxW(NULL, wmsg, wtitle, MB_ICONWARNING);
+			vim_free(wmsg);
+			vim_free(wtitle);
+		    }
+		    else
+# endif
+			MessageBox(NULL, msg, title, MB_ICONWARNING);
 		    need_vimrun_warning = FALSE;
 		}
 		if (!s_dont_use_vimrun && p_stmp)