What MediaWiki is
MediaWiki table markup opens with {| and a class, marks headers with an exclamation mark and rows with |-.
Wikipedia editors and anyone running a MediaWiki install.
What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What changes when you convert MediaWiki to Excel
Both cell styles are read: one cell per line, and several on a line separated by exclamation marks or double pipes, which is the form most Wikipedia tables use. Cell attributes before a single pipe are dropped, since style="text-align:right" is presentation rather than data. Wiki links come through as their display text, so [[France|the French Republic]] arrives as the French Republic, and reference markers are removed.
You get a single sheet with a header row and column widths sized to the content. Values are written as text unless type inference is on, which keeps identifiers like 0044 or 007 intact.
What carries over from MediaWiki to Excel
MediaWiki records 2 things about a table that Excel has no way to hold.
Excel wants a type for each column, and MediaWiki does not record one, so each column is typed from what its values look like. A column of digits that should stay text - a zip code, a phone number, a leading-zero id - is the usual thing to check afterwards.
MediaWiki can hold a value that is itself a list or an object. Excel has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
Excel has no separate idea of a header, so the column names become an ordinary first row and nothing in the file marks them as different from the data.