I'm profiling a calendar page which shows a bunch of events. I collect a profiling file and open it in https://www.speedscope.app, look at sandwich view, and see that isEnglish is the 3th slowest function (by self time) (and supportsFastNumbers is 5th):

I take a look at isEnglish :

As I'm working in Norwegian locale, I assume this returns false, but most importantly - creates new Intl.DateTimeFormat on every call.

I have not tried this yet, but I believe we can win some time if we cache Intl.DateTimeFormat (or avoid doing this check).

Same happens in supportsFastNumbers.

• OS: Win 11
• Browser: Chrome 112.0.5615.138
• Luxon: 3.3.0