There are so many language pairs you support. What sources (dictionaries) do you use for translations? Wiktionary?
Since each word might translate differently in different contexts, do you also select the most appropriate translation to display? It would be interesting to discuss about the most optimal methods for that. Google Translate often gets this wrong. (I am working on NLP/AI for language learning myself although we will mostly use it for conversations at first.) I believe many people here can give interesting perspectives on this hard problem (semantic disambiguation for translation).