I'm developing a dictionary website, and the aim is to keep things simple and clear for the users.

The dictionary is between two languages. There is a prominent search box in the header with a submit button sayings "Search the dictionary".

I've asked a couple of people to test it out. They all asked "does this search box search both languages?". They're not sure that if they type in an English word, that it will search for the translation in the other language. Or if they type in a word in the other language that they English translation will be found. (The answer is yes, it searches both directions.)

How would you suggest making it clear that a search box will search both languages?

Possible solutions:
- An info box popping up when they click on the form? (Hopefully not)
- Pre-fill the input box with a brief explanation? (Ok, but is messy again with Javascript).
- Somehow exmplain it with the submit button text?
- ... A simpler but clear solution?

Thanks.