> The problem is caused by the fact that the file installed by TexLive
> 2017 is called usenglish.ldf, not USenglish.ldf. This matters, on UNIX
> at least. Ironically, usenglish.ldf contains the line
> \ProvidesLanguage{USenglish}
I've uploaded a bug fix. It should be available soon.
Javier