Merge branch 'jc/test-i18ngrep'

With release 2.44 we got rid of all uses of test_i18ngrep and there is no in-flight topic that adds a new use of it. Make a call to test_i18ngrep a hard failure, so that we can remove it at the end of this release cycle. * jc/test-i18ngrep: test_i18ngrep: hard deprecate and forbid its use