First you need to understand the underlying structure before you can search for content. The tree node holds the pages position in the content tree. It has no idea what culture the page is because that is stored with the document information.
The document record holds the culture info as well as foreign key references to the tree node, page type info, sku info objects. With this last statement you'll see you can't get a single documents culture if you only have the tree node or nodeid. Your query needs to include the document culture as well.
Take a look at the API Examples on how to retrieve a product page. Instead of using the CombineWithDefaultCulture() you can specify the culture to retrieve. While the Node has a SKUID associated with it, you need the culture as well which is stored with the Document.