Implement and Use a Big Table of Common Words
I suspect that most common words are the "same" in all languages... So, we could do a big table, where columns are languages and rows are common words... And then we can use this big table for translations of common words between any language pair. If we do this, then we don't to rely on external translators anymore.
If we order the rows roughly by how common the word is in all languages, we can even let the user adjust the difficulty level by selecting the lowest row and the highest row that he wants to use from the table...