Incorrect birthday can be set (updated successfully dialog pops up but not actually saved)
❌操作を完了できません
✔プロフィールを保存しました

ver 11.30.0
By the way…… Born in the future is allowed? 🤣
e.g.

This is a kind of humor and I think don't need to fix it.
It seems to bring some other problems... Are these issues or by design? 🤔
And should we open new issues or just track them here?
If the date is not set before, the indicator will not display when I input an invalid date with the day not inputted in the last. (e.g. input in the following order: year-> day-> month)

The indicator text language is OS based(i.e. If I use Win10 ENU and set the set language to Japanese in the misskey settings, the indicator is still English.

The second and third items are design in my implementation. as you see, the indicator texts are depends on your browser; It doesn't matter what your OS default language is, these texts are from your browser, so If you install firefox with ja-JP locale #, it will show the messages in japanese.
I think that first (year>day>month) one is some kind of issue in browser JS side (I don't have idea how we can workaround this).
My browser locale is in English, still the date in the profile page shows in japanese
Most helpful comment
By the way…… Born in the future is allowed? 🤣

e.g.