The Japanese data point in #821 (zitann2020) offered to write its rows against whatever mechanism
this PR lands, so both languages share one catalog instead of inventing two. This makes adding a
language a data change and reserves `ja`:
- `Catalog` holds a language's effect rows and its category labels, and `catalog()` resolves a
language code to one; adding a language is two tables and one arm, with no change to the lookups
or to any panel.
- `JAPANESE_EFFECTS` and `JAPANESE_CATEGORIES` are declared, keyed by the same effect ids and by
the registry's English category names, and `ja` resolves to them. Both are empty, so a Japanese
interface draws exactly what it drew before — the slot changes no behaviour on its own.
- `a_pending_language_only_uses_known_ids` guards the pending tables (Japanese and Traditional
Chinese) as rows arrive: an id Simplified Chinese does not know, a different English name for one
of them, an empty translation or a repeated id fails. `languages_without_rows_draw_the_registry_name`
asserts each pending language has an arm in `catalog()` (a table with no arm would leave a
translator's rows dead) and is still row-less, so the day one gets rows the test says where its
coverage moved.
- `only_the_brand_names_stay_in_english` now documents that it pins *Simplified Chinese's* five
brand names and is deliberately not shared: AE's Japanese interface keeps the whole `CC`, `VR`
and `OCIO` sets in English while its Chinese one translates them, so repeating the English name
is a language's choice and not an unfinished row. The row check reflects that (a repeated English
name is accepted, an empty one is not).
docs/localization-parity.md records the two empty tables and that each language decides for itself
which names stay in English.
Refs #821
e655159382