patch 8.0.0074
Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.
diff --git a/src/spell.c b/src/spell.c
index eb81ad2..91a48fa 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -6428,7 +6428,7 @@
     sfwordnr = soundfold_find(slang, goodword);
     if (sfwordnr < 0)
     {
-	EMSG2(_(e_intern2), "add_sound_suggest()");
+	internal_error("add_sound_suggest()");
 	return;
     }