[PATCH v2] Improve the width of alternate representation for year in strftime [BZ #23758]

[Paul Eggert]

TAMUKI Shoichi wrote:
> Since only one Japanese era name is used by each emperor's reign, it
> is rare that the year ends in one digit or lasts more than three
> digits.

Rare recently, but over the long term about 75% of Japanese imperial years have 
been single-digit years: since 701 AD there have been 989 single-digit years but 
only 329 two-digit years. (This calculation is approximate, but it's close 
enough; see attached shell script for how I did the calculation.) Although Japan 
is more stable now than it was centuries ago, the long reigns since 1868 are a 
historical aberration and it should not be surprising if the fraction of 
single-digit years reverts closer to historical levels in the not-too-distant 
future.

Although I'm no expert in Japanese, as I understand it the most common style for 
formatting imperial dates in plain text uses no spaces anywhere, e.g., "平成2年3 
月4日" for Heisei 2 March 4. It's far less common to see spaces to make things 
line up, presumably for tables.

Since glibc is already defaulting to space padding for month and day-of-month, 
it makes sense for glibc to also default to space padding for imperial year. 
However, this change should be announced more clearly. The ChangeLog entry 
should say what's going on at a high level, and give an example call to strftime 
with the before-and-after output, along with how to generate imperial dates with 
no spaces; and (more important) the glibc documentation should for strftime 
should contain similar examples.
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