In farm solutions you can use resource files inside aspx-pages by deploying resx-files to the hive. MSDN have some documentation but there's no example for page layouts, just managed code which is deprecated in sandboxed solutions.

Is there a way to localize page layouts (html or aspx) in sandboxed solution without using managed code?

EDIT: I have added a request on uservoice, feel free to vote on it!