Code
T9003 unknown-message
A message whose key no language of the project has.
Details
The check holds three things to the language files:
TypeScript
<h1>{message('orders.titel')}</h1> // T9003: no language gives orders.titel
note: text({ label: message('field.note') }) // T9003 where no language gives field.note
status: choice(['open', 'paid'], { messages: 'status' }) // T9003 for each value with no message under status.<value>A message(...) whose key is written in place is held in a view and in a backend file alike, as the label and the help of a type. A key that is built from a value, as message(['status', o.status]), is held through the choice it is built from: every value of a choice that states messages has its message.
The fix
Give the key in the language files, or name a key that they give.