I am an ELL myself, and after researching and test many apps, the best apps in my opinion is google translate and dictionary.com (premium version). The following 3 websites list many apps for ELL. ...
The following apps are extremely useful tools to implement in an English as a second language classroom environment (Apple, n.d.; Williams, 2012; Writers, 2012).This website was about using Ipads in the ESL classroom. Many of the apps were great for helping students to nurture vocabulary skills. One of the apps that looked most interesting was Adventures for Kids, the app had story-based games which nurture vocabulary skills through repetition. Another app that looked interesting was the Phonetic Focus, it is one of the most popular ESL apps. It has a phonetic typewriter, games, flash cards, audio recording and playback, and many other tools to help master the English language.