Hook into you response generator or create a middleware that does the following:
res.header("Content-Type", "application/json; charset=utf-8");
Otherwise the browser displays the content in his favorite encoding.
If this doesn't help you DB is probably in the wrong encoding.
Edit: Since the answer is nearly 5 years old, the API has changed. For current node.js versions use:
res.setHeader("Content-Type", "application/json; charset=utf-8");
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