The current "title" of the extensions guide is "Basic Knowledge"...

Note that a contribution from a Japanese speaking maintainer would still be needed for this ; there are two headings that need translation:

• "Creating Extension Libraries for Ruby" (new document title)
• "Example - Creating the dbm Extension" (was missing in the ja version)

I guess there is no shortage on developers who are able to use written japanese AND written
english. :)

Thanks for the translation, kazu!