Japanese now translates the status-bar and error messages (`@msg`
templates) like Spanish, French, Italian, Russian and Ukrainian do:
556 rows at the end of ja.tsv, the 498 message literals the test scan
finds plus the 58 that the other catalogs also carry (web start-up,
relinking, export notes, PostScript read errors).
`ja` joins COMPLETE_MESSAGES, so complete_languages_translate_every_message
keeps it complete. The registry comment, docs/development.md and the
ROADMAP line now list Japanese with the other five. The messages
themselves stay English for agents and MCP.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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