Talend: how to export a formatted Date field to xlsx and import it back again

With talend I'm reading from a tSalesforceInput and exporting to a tFileOutputExcel. Inbetween there is a tMap just passing through all fields.

In a second step I want to use the locally written xlsx file for an tFileInputExcel and use it as a Lookup for a tMap.

I perfectly works - as long I avoid Date fields. Once I add one datefield to the schema, I'm getting many line of error-output like this:

...
The cell format is not Date in ( Row. 1 and ColumnNum. 13 )
The cell format is not Date in ( Row. 1 and ColumnNum. 13 )
The cell format is not Date in ( Row. 1 and ColumnNum. 13 )

The Salesforce Date Pattern is "yyyy-MM-dd'T'HH:mm:ss'.000Z'" and its used consistently at all schemas.

Any idea on how to reimport dates in this format? Is it because Excel it treating it not as Date but as String? Possibly a CSV would help, but I would prefer not using a CSV, because it's hard to deal with if you are using a German locale...