patch 8.2.2847: Perl not tested sufficiently

Problem:    Perl not tested sufficiently.
Solution:   Add test.  Also test W17. (Dominique Pellé, closes #8193)
diff --git a/src/testdir/test_arabic.vim b/src/testdir/test_arabic.vim
index 2729373..73b85c4 100644
--- a/src/testdir/test_arabic.vim
+++ b/src/testdir/test_arabic.vim
@@ -584,4 +584,12 @@
   bwipe!
 endfunc
 
+func Test_W17_arabic_requires_utf8()
+  let save_enc = &encoding
+  set encoding=latin1 arabic
+  call assert_match('^W17:', GetMessages()[-1])
+  set arabic&
+  let &encoding = save_enc
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab