i18n: use test_i18n{cmp,grep} in t7600, t7607, t7611 and t7811

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 87d5d78..e84e822 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -495,10 +495,10 @@
 
 test_debug 'git log --graph --decorate --oneline --all'
 
-test_expect_success C_LOCALE_OUTPUT 'in-index merge' '
+test_expect_success 'in-index merge' '
 	git reset --hard c0 &&
 	git merge --no-ff -s resolve c1 >out &&
-	grep "Wonderful." out &&
+	test_i18ngrep "Wonderful." out &&
 	verify_parents $c0 $c1
 '