Mark, all .xml files in the lang directory will be monitored by EPiServer, and the XML information from each one will be merged into a single XML DOM (Document Object Model). What that means is, you can have ALL your language information (for ALL languages you need to support) in a single xml file. Or you could decide to use different files, perhaps one for each language and/or separating into separate files based on the context for the texts. What is important is the XML structure itself. Just mimic the structure used in the existing files, for the languages and language elements. Below that point, you can create an XML structure to your liking. If you want to "override" any existing translations withuot having to modify the existing files, you can simply mimic the entire XML structure used for that particlar translation in a new file, and enter your custom translation there. When doing so, you need to be aware that the files are read in alphabetical order by EPiServer (so any overrides need to be read after the original texts).