From HandWiki
Short description: Glyph used as an apostrophe or a quotation mark

The Unicode character (U+2019 RIGHT SINGLE QUOTATION MARK) is used both for a typographic apostrophe and a single right (closing) quotation mark.[1] This is due to the many fonts and character sets (such as CP1252) that unified the characters into a single code point, and the difficulty of software distinguishing which character is intended by a user's typing.[citation needed] There are arguments that the typographic apostrophe should be a different code point, U+02BC MODIFIER LETTER APOSTROPHE.[2]

The straight apostrophe ' (U+0027 APOSTROPHE) is even more ambiguous, as it could also be an open quotation mark, or a prime symbol.

References