Use Locale for determinating I18N values

[pleku]

After vaadin/vaadin-date-picker-flow#38, the component will have locale support for displaying the selected date value, but it is not applied to the date picker popup, which is localized via the properties in the DatePickerI18N object.

The set locale should be used for figuring out the following properties for the DatePickerI18N object:

• month names
• weekdays
• weekdays short
• first day of week

Acceptance Criteria

• the locale set for the component on server side controls the properties described above
• the user is still able to override those for the I18N object

[nemojmenervirat]

the user is still able to override those for the I18N object

it would be nice to override this only once and every date picker in UI will have new I18N object, instead of setting I18N object for every instance of date picker

[nbruck]

Just want the mention that the picker popup need to display also the correct year in case the locale is changing the year due to Transformation from gregorian calender to buddhist for example.

[web-padawan]

Related issue in the web component (let's keep both open for now): vaadin/web-components#3383

[Frettman]

Just like the date pattern, the four properties mentioned in this issue can be determined automatically based on the locale (with information already provided by Java), which would help a lot and only leaves a few labels to be translated.

The following code determines the four properties based on locale. Unfortunately there's no hook to automatically set this; or update it in case of a locale change. But might still be useful to some:

DatePicker.DatePickerI18n i18n = new DatePicker.DatePickerI18n();

i18n.setFirstDayOfWeek(WeekFields.of(locale).getFirstDayOfWeek().getValue() % 7);

i18n.setMonthNames(Stream.of(Month.values()).map(m -> m.getDisplayName(TextStyle.FULL_STANDALONE, locale))
    .collect(toList()));

List<String> weekdays = Stream.of(DayOfWeek.values())
    .map(d -> d.getDisplayName(TextStyle.FULL_STANDALONE, locale)).collect(toList());
Collections.rotate(weekdays, 1);
i18n.setWeekdays(weekdays);

List<String> weekdaysShort = Stream.of(DayOfWeek.values())
    .map(d -> d.getDisplayName(TextStyle.SHORT_STANDALONE, locale)).collect(toList());
Collections.rotate(weekdaysShort, 1);
i18n.setWeekdaysShort(weekdaysShort);

[mstahv]

@Frettman Your code is awesome 😍 I changed it slightly, so that it also works with weird languages, like the one we speak here in Finland. Then integrated into VDatePicker and VDateTimePicker in Viritin. They now read proper settings from active locale 😎:

viritin/flow-viritin@0f887f7

Available in in.virit:viritin:1.3.0 as soon as Maven central gets synchronised.

[Frettman]

@mstahv Glad it was useful :) There's one thing I should add though: WeekFields#getFirstDayOfWeek only works if the locale contains a country. Otherwise it falls back to Sunday being the first day of the week, which e.g. for de doesn't really make sense. So for locales without country I'm experimenting with just picking the first locale from Locale.getAvailableLocales() with the same language that has a country. Certainly not perfect and might get it wrong as much as it gets it right. The only save way would be to make sure all used locales contain a country. Certainly out of scope for your add-on but might be worth adding to the Javadoc somewhere or even a warning that's logged once :)

[mstahv]

Yup, complete locale is needed indeed. I have no idea how common it is to use locales without country and if that is on purpose or not. Depending on that, it might be that the additional logic you described would make sense.