The best way to teach abstract concepts is with a multi-sensory approach. In many cases, abstract language can be better represented with pictures. If those pictures also have other interactive qualities that will create a higher level of engagement. If a child can touch the screen and can interact, then the child will have other means to express themselves through actions.
Category Therapy
Being able to put information in a category is an important part of any language. The concept is abstract and can be difficult to teach.
https://itunes.apple.com/us/app/category-therappy/id571551926?mt=8&ign-mpt=uo%3D4
Website: http://tactustherapy.com/apps/
Little Stories Pro
This app has short high-interest stories that teach a specific area of language. The app gets very good ratings.
https://itunes.apple.com/us/app/little-stories-pro/id1228283813?mt=8
Multiple Meanings Library
This app teaches multiple means. The English language has so much creativity that it is hard for some to grasp. The app is designed for speech and language pathologists, but I see it being useful for people that are learning English as a second language.
https://itunes.apple.com/app/multiple-meanings-library/id525605265
Conversation Therapy
This app is designed to teach higher-level expressive languages. The ability to have a conversation is difficult to teach.
https://itunes.apple.com/us/app/conversation-therappy/id620456076?mt=8
Company’s YouTube.com Channel: http://www.youtube.com/user/tactustherapy?feature=watch
Naming Therapy
This app teaches commonly used names in different contexts. The app has a lot of different ways to teach names. The app also tests the user.
https://itunes.apple.com/us/app/naming-therappy/id451093640?mt=8
Antonyms
This is a visual, game app that teaches antonyms.
https://itunes.apple.com/us/app/antonyms/id642104434?mt=8
Categories Learning Center
This app teaches the abstract concept of categories.
https://itunes.apple.com/us/app/categories-learning-center/id496646536?mt=8
RadSounds
This is a very cool app. The app teaches cause and effect with music and funny characters. It is so simple that it is what makes it brilliant.
https://itunes.apple.com/us/app/radsounds/id420977569?mt=8
Verbal Reasoning
This app challenges you to use abstract language.
https://itunes.apple.com/app/verbal-reasoning/id604097479