Please open a case with Tableau Support so they can take a deeper look at the issue. If you can provide the Excel file being used - Support should be able to figure out why this collation error is occurring.
I am testing Tableau 10.5 and while searching the forums for potential issues I found the following thread which sounds like it may be the same problem you are experiencing: https://community.tableau.com/thread/256776
A workaround posted in that thread by Chip Felton was to: change text file locale to "English (United States)" in the Data Source Pane (right click on table after dragging the text file into the middle of the pane, choose "Text File properties").
Perhaps this will also work for your situation while waiting for an actual fix from Tableau.