Sanity field-level i18n arrays and preferredLocale, who resolves the language?
We run a Norwegian public sector site where documents store translations as internationalized arrays per field, so a title is [{_key: "nb", value: "..."}, {_key: "nn", value: "..."}, {_key: "en", value: "..."}].
I am reading the Croct docs and see that fetches accept a preferredLocale option. What I cannot work out is the division of responsibility. If I pass the whole i18n array as the fallback, does anything resolve it? Or should my code pick the locale value first and pass a flat object?
Language fallback chains matter a lot for us (nn falls back to nb, never to en), so I want the resolution to happen in exactly one place.
2 answers
Resolve the array yourself, before the slot fetch. The preferredLocale option tells Croct which locale's variant content to serve for the slot, but it does not know anything about Sanity's i18n array structure, that is a convention of your dataset, not a content format Croct parses.
So the clean split is: your code resolves the i18n array to the active locale (applying your nn to nb fallback chain), producing a flat object, and that flat object is what you pass as the fallback. Then both sources render identically: Croct-served content is already in the requested locale, and the fallback is too. Your locale logic lives in exactly one function, which sounds like what you want.
If you pass the raw array as fallback, the component either needs to handle two shapes or breaks when the fallback kicks in, which is the worst possible time to discover it.
Adding the other half of the picture: on the Croct side, per-locale default content (the localization feature) is an add-on, but you may not need it for your setup. Multi-language works without extra dev because the localized Sanity value remains the per-locale fallback, so each locale already renders the right default through your own resolution. The add-on matters when you want locale-specific defaults managed inside Croct itself rather than falling back to what your code passes in.