Answers

Looks like this may have been someone's remedy for a deteriorated / rotten mud sill (the flat wooden plate which sits atop the foundation wall, upon which the joists bear).  If that is the case, it is possible that you might be able to remove the latter obstruction if one can restore the proper / original condition over the window.  That would want to be examined and undertaken by a professional.

As with any such thing, it is difficult to say for sure without a full on-site examination by a home imporvement professional with structural knowledge and experience in these types of repairs.