Lint rules
invalid-locale
errorFlags a messages file whose locale the runtime doesn't recognize.
Why this is bad
The Intl APIs resolve an unknown tag to the runtime's default rather than rejecting it, so plural rules, number formats, and dates all quietly come out as the default locale's.
Examples
The locale comes from the filename, so a name the runtime can't parse is incorrect.
Examples of incorrect code for this rule:
messages/
spanish.json
Examples of correct code for this rule:
messages/
es.json