Bug report

It is broken in the same way as locale.nl_langinfo(locale.ALT_DIGITS) was broken (see #124969), although not to the same degree. It returns the last (current) era.

import locale, subprocess
alllocales = subprocess.check_output(['locale', '-a']).decode().split()
for loc in alllocales:
    if '.' in loc or '@' in loc:
        continue
    try:
        _ = locale.setlocale(locale.LC_ALL, loc)
    except locale.Error:
        continue
    era = locale.nl_langinfo(locale.ERA)
    if era:
        print(loc, era)

Output:

cmn_TW +:2:1913/01/01:+*:民國:%EC%Ey年
hak_TW +:2:1913/01/01:+*:民國:%EC%Ey年
ja_JP +:2:2020/01/01:+*:令和:%EC%Ey年
japanese +:2:2020/01/01:+*:令和:%EC%Ey年
lo_LA +:1:-543/01/01:+*:ພ.ສ.:%EC %Ey
lzh_TW +:2:1913/01/01:+*:民國:%EC%Ey年
nan_TW +:2:1913/01/01:+*:民國:%EC%Ey年
thai +:1:-543/01/01:+*:พ.ศ.:%EC %Ey
th_TH +:1:-543/01/01:+*:พ.ศ.:%EC %Ey
zh_TW +:2:1913/01/01:+*:民國:%EC%Ey年

The result is not completely useless, as it can be used to format and parse the current dates. But dates before the start of the current era (it is 2020 in Japan) cannot be proceeded.

The result should be a tuple, containing information for all eras, but this is a breaking change. So, perhaps such change cannot be backported.

cc @methane