Lint rules
undefined-key
errorFlags a key your source code references that the source locale doesn't define. Only applies when srcPath is set, and currently only supports next-intl.
Why this is bad
There is no message to render, so rendering may fail or use a fallback.
Examples
Given source code that calls t('discard').
Examples of incorrect code for this rule:
messages/en.json
{"save": "Save"}
Examples of correct code for this rule:
messages/en.json
{"save": "Save","discard": "Discard"}