throwOnFallback property
If a message is looked up before any locale initialization, record it, and throw an exception with that information once the locale is initialized.
Set this during development to find issues with race conditions between message caching and locale initialization. If the results of Intl.message calls aren't being cached, then this won't help.
There's nothing that actually sets this, so checking this requires patching the code here.
Implementation
static final bool throwOnFallback = false;