Is [admin / admin] acceptable for all local websites?

As @montrealist says, using an insecure username and password combination on a local webserver installation that is not publicly accessible is not necessarily a security concern.

If the server is publicly accessible, a secure username and password should be used of course.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)