This paper discusses a novel probabilistic synchronous TAG formalism, synchronous Tree Substitution Grammar with sister adjunction (TSG+SA). We use it to parse a language for which there is no training data, by leveraging off a second, related language for which there is abundant training data. The grammar for the resource-rich side is automatically extracted from a treebank; the grammar on the resource-poor side and the synchronization are created by handwritten rules. Our approach thus represents a combination of grammar-based and empirical natural language processing. We discuss the approach using the example of Levantine Arabic and Standard Arabic.