Wikipedia:Styletips/23

Quotations: allowable typographical changes

Although the requirement of minimal change in direct quotations is strict, a few purely typographical elements of quoted text should be conformed to English Wikipedia's conventions without comment. These include the following:

Use the style chosen for the article: unspaced em dash or spaced en dash.
Set apostrophes and quotation marks straight, not curly.
Remove spaces before punctuation such as periods, colons, and %.
When integrating the quotation into the grammar of a larger sentence, downcase the first letter of a quotation that is in upper case purely because it starts a sentence in the source (It turned out to be true that "a penny saved is a penny earned").

But generally preserve bold and italic face, and the variety of English.