Low-quality and Second-class

Second-class and low-quality are semantically related in inferior topic. In some cases you can use "Second-class" instead an adjective phrase "Low-quality".

Second-class adjective - Of little or less value or merit.

Low-quality and second-class are semantically related in better topic. You can use "Low-quality" instead an adjective phrase "Second-class", if it concerns topics such as inferior.