There are so many apps to choose from that it can overwhelming. Here are a few that include Thai translations.

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5000 English Phrases - This app as a variety of activities for learning a wide range of phrases and short sentences.

6000 English Words - The easy level is good for beginners that are still learning how to read.

AnkiDroid - This is the best spaced repetition app that I've found. It has lots of user created content. The Android version is free.

Duolingo - This is one of the most popular free apps for learning languages.