As mentioned by Nakamura-san in another responce document, the deliverable of this project is planned to be able to use in English environment and user interface as well.
In terms of your participation, communication might be issue. I acknowledge that Open source project should be carried in English so that many people could participate. But in case of project being conducted by Japanese mainly, Japanese would be better as to language. Especially this is the first OpenNTF.org project running by Japanese. In order to success this project from the point of this view, ease of communication is crucial.
After all , your input would be appreciated even if in English.
Would you like to participate ?
Best regards.