The sentences tab in the dictionary allows both English and Japanese search terms, but it has a tendency to interpret English search terms as romaji Japanese search terms. It would be nice to have a way to only search the Japanese sentences or only the English translations, instead of both like currently happens.
This has been added in beta. It's the little settings icon next to the search button. The setting persists across page loads, so it'll keep your preference after you set it once.
