java.util.Date and java.util.Calendar are not deprecated, and still work as they always have. However, how they work is difficult to use, which is why java.time classes are recommended instead.

What you are seeing is the difference between WEEK_OF_YEAR (which depends on the locale) and ALIGNED_WEEK_OF_YEAR (which is the same in all locales).

When setting or getting the WEEK_OF_MONTH or WEEK_OF_YEAR fields, Calendar must determine the first week of the month or year as a reference point. The first week of a month or year is defined as the earliest seven day period beginning on getFirstDayOfWeek() and containing at least getMinimalDaysInFirstWeek() days of that month or year. Weeks numbered ..., -1, 0 precede the first week; weeks numbered 2, 3,... follow it. Note that the normalized numbering returned by get() may be different. For example, a specific Calendar subclass may designate the week before week 1 of a year as week n of the previous year.

ALIGNED_WEEK_OF_YEAR represents concept of the count of weeks within the period of a year where the weeks are aligned to the start of the year. This field is typically used with ALIGNED_DAY_OF_WEEK_IN_YEAR.

For example, in a calendar systems with a seven day week, the first aligned-week-of-year starts on day-of-year 1, the second aligned-week starts on day-of-year 8, and so on. Thus, day-of-year values 1 to 7 are in aligned-week 1, while day-of-year values 8 to 14 are in aligned-week 2, and so on.

And for the locale difference:

// returns DayOfWeek.MONDAY
WeekFields.of(Locale.forLanguageTag("de-DE")).getFirstDayOfWeek();

// returns DayOfWeek.SUNDAY
WeekFields.of(Locale.forLanguageTag("en-ZA")).getFirstDayOfWeek();

To get the unaligned week of year using the current system local with java.time:

LocalDate.now().get(WeekFields.of(Locale.getDefault()).weekOfYear())

If you want to be locale-independent, then there is ISO.weekOfYear() if you want the week to start on a Monday, and SUNDAY_START.weekOfYear() for a Sunday.