sql filter by language

Just to provide an example, I'm using some made up tables. It's actually doing an intermedia search through two clobs, but that's irrelevent. The basic structure is the same, but I need to provide a filter based on language. Basically, what I want is to be able to search on one column, regardless of language. But when I find a record that matches, I want to return it in the language of choice. However, if it doesn't exist in that language, then still return it in the other language. So using my fake tables below, if I was looking for book and I wanted it returned in french, then it would find productId number 2, but it would return the entry that is in french. The twist is that if I was looking for pen, which doesn't have a french entry, then I need to return the english entry.

select productName from productTable
where //pseudo-code//preferredLanguage = 'french' and productTable.productId in
(select productId from secondProductTable where secondProductTable.description = 'book')

I was thinking of some group by using having sum, or something along those lines. This has to be sql, not pl/sql. thanks

productTable

productId	productLang 	productName
1		english		chairName
1		french		chaiseNom
2		english		bookName
2		french		livreNom
3		english		penName
4		english		paperName
4		french		papierNom

secondProductTable

productId	productLang 	productDesc
1		english		chair
1		french		chaise
2		english		book
2		french		livre
3		english		pen
4		english		paper
4		french		papier