In spite of its popularity, XML provides poor user experience and a lot of domain-specific languages can be improved by introducing custom, more humanfriendly notation. This paper presents an approach for design and development of the custom notation for existing XML-based language together with a translator between the new notation and XML. The approach supports iterative design of the language concrete syntax, allowing its modification based on users feedback. The translator is developed using a model-driven approach. It is based on explicit representation of language abstract syntax (metamodel) that can be augmented with mappings to both XML and the custom notation. We provide recommendations for application of the approach and demonstrate them on a case study of a language for definition of graphs.