The batched translation preload requires the (tableName, recordNum,
prefix) index; without it the per-record query scans and is slower
than the legacy per-field lookup. t() now checks once per PHP process
(static) whether idx_tabla_registro_prefijo exists, creates it on the
fly when the DB user has ALTER rights (re-checking after a lost race),
and otherwise falls back to the legacy per-field query — never slower
than the original behavior on webs where the index cannot be created.
Verified live: dropped the index on villagrancanaria local, first
request recreated it automatically and subsequent renders stayed fast.
34d1458f3a