In some languages, a month name that is part of a date appears in the genitive case. For example, a date in the ru-RU or Russian (Russia) culture consists of the day number and the genitive month name, such as 1 Января (1 January). For these cultures, if a custom format string includes the "MMM" format specifier, the DateTime.ToString or ToString method includes the appropriate member of the AbbreviatedMonthGenitiveNames array in place of the "MMM" in the result string.
This means when formatting a date containing the day as a number (i.e. using d or dd in the date pattern), then the genitive names will be used. As you are using the date pattern d.MMM.yyyy, this means the date will be formatted using the genitive month names. You will get a formatted date something like 1.Jan..2020. Note the genitive month name here is Jan. and not Jan. If you parse back the formatted string 1.Jan..2020 this will be parsed fine. You are not parsing the formatted string instead you are parsing your constructed string 1.Jan.2020 which is not a correct form. If you want to get the result you want with de-DE, you may use something like d.MMMyyyy or you format with day names instead of day number, like ddd.MMM.yyyy
Possible solution
You could use the invariant culture to get the result you are looking for:
new DateTime(2022, 6, 21).ToString("ddd MMM dd yyyy", CultureInfo.InvariantCulture)
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评论（1）
tl; dr;
使用不变文化，如果您总是想获得
jun：更长的解释
真的很有趣，为什么（有时）发生这种情况。
您应该检查您使用的文化的
缩写的monthgenitivenames。重现它，
您可以重现行为，当您使用具有缩写的月份名称的文化时，与默认值不同：
解释
有一个解释在
abbreviatedMonthgenitivenames的文档中和也有一个问题也提到了这一点：
可能的解决方案
您可以使用不变文化来获取您要寻找的结果：
此结果：
tue> tue> tue>TL;DR;
Use the invariant culture, if you always want to get
Jun:Longer explanation
That's really interesting why this happens (sometimes).
You should check the values of your
AbbreviatedMonthGenitiveNamesof the culture you're using.Reproduce it
You can reproduce the behavior, when you use a culture with abbreviated month genitive names that differ from the default:
Explanations
There is an explanation in the documentation of
AbbreviatedMonthGenitiveNames:and there is an issue where this is mentioned too:
Possible solution
You could use the invariant culture to get the result you are looking for:
This results in:
Tue Jun 21 2022