Add new optional and ignored messages in core

* Optional interlanguage-link-title-nonlang
* Ignore interlanguage-link-title-nonlangonly

These messages were introduced in
I3d04760e2d9fb3320bb71e3d5ad115eed54a899c

Change-Id: If5e94bebbad377beefafd74c8efa7f46799704bb