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 CSV is
CSV is a text file where each line is a row and commas separate the fields. There is no type system, no formatting and no second sheet. Every value is text until something downstream decides otherwise.
Almost every database, analytics tool and spreadsheet can read and write it, which is why exports default to it.
What changes when you convert MediaWiki to CSV
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.
Any value containing the delimiter, a quote or a line break gets wrapped in quotes, and embedded quotes are doubled. That is the rule in RFC 4180 and it is what spreadsheet software expects.
Wiki links become their display text. A cell containing [[France|the French Republic]] arrives as the French Republic, and one containing [[Paris]] arrives as Paris. The target of the link is markup rather than the value, so it does not survive.
Reference markers are removed. A Wikipedia cell often carries a <ref> block that renders as a small numbered footnote, and leaving it in puts a chunk of citation metadata in the middle of your data.
Cell attributes are dropped. A cell written as | style="text-align:right" | 42 arrives as 42, because the alignment describes how the cell looks rather than what it holds.
Bold and italic markers go. Wikipedia uses apostrophes for both, and a value that arrives as '''Total''' is not a value anybody wants.
What carries over from MediaWiki to CSV
MediaWiki records 3 things about a table that CSV has no way to hold.
MediaWiki can hold a value that is itself a list or an object. CSV has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
CSV 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.
Anything visual in the MediaWiki - weight, alignment, colour, column widths - has no counterpart in CSV and is dropped. The values are what survives.
The result can be read a record at a time, and appended to by adding to the end of it. That is worth having for a table too large to hold in memory, and it means a CSV file that is cut off part way through still gives you every record before the cut.
The identifier 007 comes out of the CSV as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.
The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a CSV file goes wrong.
The quotes around Jonah "Jo" Pryce are doubled, which is how the delimited formats escape a quote in the CSV.
Getting the markup in the first place
On any Wikipedia article, use Edit source rather than Edit. That shows the wikitext, and a table in it starts with a brace followed by a pipe.
If you would rather not go looking, paste the article URL into the address box in the converter above instead. That fetches the rendered page and pulls the tables out of the HTML, which for Wikipedia gives the same result with fewer steps.