Very trivial bug that I noticed a couple of versions back and I see is still in Version 184.108.40.206.
Reports -> Data Dictionary Reports -> Database Administration -> Storage -> Datafiles
the 'tablespace' column is labelled 'tablspace' i.e. missing an 'e'.
Thanks for reporting the typo. It is inline in the SQL itself and so does not undergo any of the usual NLS translation. Typos usually get caught at that level if we miss them. Fix checked in for the next patch (whenever that may be).
SQL Developer Team