https://english.stackexchange.com/questions/17695/any-reference-on-the-usage-of-a-backtick-and-single-quotation-mark-like-this#17696
Basically, as answered by @mgkrebbs, quotations like 'this' or `this' are faulty typographic usage introduced with limited character sets, first with 19th century typewriters then with digital character encoding. The proper (Unicode) characters are ‘these’. The same happens with apostrophe and primes (for feet and inches). One should type
“Alice’s friend told me ‘My son is 6′3″ tall.’”
instead of
"Alice's friend told me 'My son is 6'3" tall.'"
But it's easier said than done.
For reference about these various "apostrophes" I've found the following documents:
- The official version : The Unicode standard 6.0.0 (the last version as of today), more specifically the chapter 6 Writing systems and punctuation (pdf) sections Language-Based Usage of Quotation Marks, Apostrophe p188-191 (12-14 of the pdf)
- A paper by Michael Everson written in 1999, On the apostrophe and quotation mark, with a note on Egyptian transliteration characters, submitted as working group document N2043 to the Unicode consortium.
- A webpage by Markus Kuhn, written roughly simultaneously in 1999 which explicitly discourages quotations `like this', with explanation on how and why these quotation appeared. Both Markus and Michael were involved in a thread on Unicode mailing list in 1999 about this problem, hence the two simultaneous paper.
- Languagegeek also has a nice write-up on various apostrophes and quotation marks in the context of native English and American languages like Hawai‘ian.
Of course, all this is mainly on English. Digressing further away from your question, you have other interesting things like the Mè'phàà language of Mexico, which uses the straight quote as a casing letter (pdf), with both a lower case ꞌ and an upper case Ꞌ version, both added in Unicode 5.1.
https://en.wikipedia.org/wiki/Prime_(symbol)
