This was already answered in your ticket, but since you double-posted (please do not do in the future):
Language files can only control text elements within a page. Anything that is stored in the database can not be controlled by language text files... but must be handled by a component. DT Register supports multi-language using the FaLang component, which is free. Set that up, then install the DT Register Falang elements zip file (inside the DT Reg package)... which gets installed in the Falang component, not in Joomla's extension manager. Then you'll be able to control multi-language for custom fields, event names, locations, categories and everything else that is stored in the database.
Nathan is no longer affiliated with DTH since the recent acquisition. You can connect with him and get any type of Joomla website help at
www.JoomlaEmployee.com
.