NOTE:The non-public cause of this is known and is being worked on.
https://en.m.wikipedia.org/wiki/Battle_of_Trenton
{F31962333}
I can't replicate this locally but it seems to be occurring across the wiki.
= Developer notes
Following works fines:
```
mw.messages.set('test1', '[[Special:Block]] $1.' );
mw.message( 'test1', 'test' ).parse();
```
The following doesn't:
```
mw.messages.set('test1', '[$1 a]' );
mw.message( 'test1', 'test' ).parse();
```
The following does
```
mw.messages.set('test1', 'a [https://foo A]' );
mw.message( 'test1', 'test' ).parse();
```
The following doesn't work on production but does locally:
```
mw.messages.set('test1', 'a [$1 A]' );
mw.message( 'test1', '/wiki/Foo' ).parse();
```
Under the hood this message uses mw.util getUrl - I'm not sure if previously that returned an absolute URI but it appeared to return a relative URI.
Technically `[/wiki/Foo test]` is invalid wikitext so it makes sense this is failing but it's not clear what has changed to cause this and break this in production.