http://ritsuchan.i2p/faq.html
If the language is "plain", an unsupported value, or the auto-detect confidence is too low, highlighting is disabled for the code block.
If the language is "aa", the font will be adjusted for Japanese Shift JIS art. What is the file size limit? Max size of form data per-post is 40MB. Because other fields e.g. name, message, etc contribute to this, the maximum size of file uploads will be very slightly smaller than this.