Translate Chichewa-English-Chewa Online for Free
You'll have to wade your way through quite a lot of ads, but if you're looking for a way to translate Chewa to English online for free, Freelang.net has what you need. You can also translate from English to Chewa (also known as Nyanja) using the same page.
Download Free Chichewa Dictionary and Word List for Windows
I have not tested this myself, but Freelang.net also offers free downloads of the Chewa-English-Chewa Dictionary and a Chichewa word list. This is currently only available for Windows.