OptionalmessagesCall-site messages (command chrome, dialogs, and model-layer text such as the SDK's condition
titles) — the host-pack twin of a package's locales/<tag>/messages.json slice, and the
app-level override hook: it outranks every package slice in the lookup chain.
The BCP-47 tag this pack translates to.
A language pack — plain data, no runtime dependencies. English is not a pack: the inline literals in the source are the
encatalog, so a missing key (or a missing pack) always falls back to the authored English.This base interface carries only the GENERIC plane (
tag+messages). Domain planes are added by the packages that own their types via module augmentation — the SDK augments it with the spreadsheet-language fields (functions,errors,booleans,functionHelp— see@sheetxl/sdk'sSpreadsheetLanguagePack), typed against the real descriptor shapes it can see. One runtime object, no shape copies, and this package never reaches above itself in the dependency graph.