SimpleDateFormat working on Non-English Locale(Nepali or Devnagari)

Not an 'answer' as such but worthwhile to show the correct way of dealing with your non-ISO-compliant datetime strings, avoiding the use of obsolescent classes. Thanks to user85421 for the correct way to deal with localisation for the Devangari digits:

import static java.time.format.DateTimeFormatter.ISO_DATE;
import static java.time.format.DateTimeFormatter.ISO_TIME;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;

public class NepalTimeParser {
    public static void main(String[] args) throws Exception {
        DateTimeFormatter dtfNepali = new DateTimeFormatterBuilder().append(ISO_DATE).appendLiteral(" ")
                .append(ISO_TIME).toFormatter().localizedBy(Locale.of("ne", "NP"));
        String parsingDate = "२०२४-११-३० १२:५१:४६";
        if (args.length > 0) {
            parsingDate = args[0];
        }
        LocalDateTime ldt = LocalDateTime.parse(parsingDate, dtfNepali);
        System.out.println(ldt);
    }
}

If I got the question right, all answers so far (first one, second one) do not come close to the desired answer.

My understanding is, that the thread opener was surprised that the method SimpleDateFormat::parse is able to handle non-arabic digits.

Which number signs (characters for digits) are valid digits is not related to the current Locale selected – the TO confirmed that they did not use the Nepali Locale, one comment says that the result was the same for the German Locale. It is just a definition made by Unicode which character is a numerical character.

And obviously does the parse() of java.text.SimpleDateFormat translate each valid numerical character properly to its numerical value before it tries to parse the String as a date/time value. That's a nice feature to have …

That the methods and APIs dealing with java.util.Date are long time outdated is true, but completely unrelated to the question. Not to mention that the trick does not work with java.time.format.DateTimeFormatter.

In simple terms, SimpleDateFormat knows a Locale, and unless you explicitly set it to something different, it will be your system's default Locale. It uses that Locale when parsing or formatting dates, which is what you're seeing here.

Of course SimpleDateFormat has been obsolete for almost 12 years now, and you should be using the java.time equivalent class, which is DateTimeFormatter. This class also knows a Locale, so it should act the same way (although I've never tried it in Nepal).