It would depend on the type of language that you want to learn. There are some applications that will help you learn how to speak Korean. There are also other applications that will teach you how to speak French. Each application has its own speciality so this is something that you need to be sure about.
Find an application that will not only teach you the terms but will actually help you converse with other people well. This will make it easier for you to integrate the new things that you are learning to your lifestyle. When learning a new language, you need to remember that it will become a part of your life otherwise, you will never learn.
The best app by far is Duolingo. I have learned the basics of French in 6 months as it allows you to conversate with a CPU in the language you want to learn with helpful tips. This has allowed me to learn french quicker than any class did.