Quotation mark inconsistency in English lessons

[joulev]

In more-01: “…” is used. However, in all other pages (it seems, not 100% sure) '…' is used.

What should be preferred?

(The current Vietnamese version also has some inconsistency, I will follow the one chosen here.)

[amunn]

Single quotes are most appropriate for most of the uses we need on the site, since they're usually reference to words not part of the sentence rather than actual quotations.