Matplotlib tick label localization

matplotlib tick label localization.py

import locale
import platform

import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np

dates = np.arange(np.datetime64('2022-12-01'), np.datetime64('2022-12-02'), np.timedelta64(1, 'h'))
values = np.zeros_like(dates, dtype=int)

def plot(title):
    fig, ax = plt.subplots(figsize=(6, 1.5), layout='constrained')
    ax.plot(dates, values, 'white')
    ax.xaxis.set_major_formatter(mpl.dates.ConciseDateFormatter(mpl.dates.AutoDateLocator()))
    ax.text(.5, .5,
            f"{locale.getlocale() = }\n{ax.yaxis.get_major_formatter().get_useLocale() = }\n({platform.system()})",
            transform=ax.transAxes, ha='center', va='center')
    ax.set_title(title)
    fig.savefig(title + '.png')

# use \N{MODIFIER LETTER COLON} instead of regular colon for Windows file names
plot('1꞉ default')

with mpl.rc_context({'axes.formatter.use_locale': True}):
    plot('2꞉ axes.formatter.use_locale = True')

locale.setlocale(locale.LC_ALL, '')
plot("3꞉ setlocale(locale.LC_ALL, '')")

with mpl.rc_context({'axes.formatter.use_locale': True}):
    plot("4꞉ axes.formatter.use_locale = True after setlocale(locale.LC_ALL, '')")

Matplotlib 3.6.3 on Windows:

1꞉ default--> should be Dez instead of Dec

2: axes.formatter.use_locale = True --> should be 0,00 instead of 0.00

3: after setlocale(locale.LC_ALL, '') --> this works correctly

4: axes.formatter.use_locale = True after setlocale(locale.LC_ALL, '') --> this works correctly too

import inspect
import string
import subprocess
import sys
import matplotlib as mpl

script = string.Template(inspect.cleandoc("""
    import locale
    import sys

    import matplotlib as mpl
    import matplotlib.pyplot as plt


    try:
        print('$backend', end=': ')
        locale.setlocale(locale.LC_ALL, 'en_US.utf8')
        old_locale = locale.setlocale(locale.LC_NUMERIC)
        mpl.use('$backend')
        plt.subplots()
        new_locale = locale.setlocale(locale.LC_NUMERIC)
        print(f'left {old_locale} unchanged' if new_locale == old_locale else f'changed locale from {old_locale} to {new_locale}')
    except Exception as ex:
        print(f'raised {type(ex).__name__}')
    """))

for backend in mpl.rcsetup.all_backends:
    cp = subprocess.run([sys.executable, '-c', script.substitute(backend=backend)], capture_output=True)
    print(cp.stdout.decode().strip()) 

Output on Windows:

GTK3Agg: changed locale from en_US to de_DE
GTK3Cairo: changed locale from en_US to de_DE
GTK4Agg: changed locale from en_US to de_DE
GTK4Cairo: changed locale from en_US to de_DE
MacOSX: raised ImportError
nbAgg: left en_US unchanged
QtAgg: left en_US unchanged
QtCairo: left en_US unchanged
Qt5Agg: left en_US unchanged
Qt5Cairo: left en_US unchanged
TkAgg: left en_US unchanged
TkCairo: left en_US unchanged
WebAgg: left en_US unchanged
WX: changed locale from en_US to C
WXAgg: changed locale from en_US to C
WXCairo: changed locale from en_US to C
agg: left en_US unchanged
cairo: left en_US unchanged
pdf: left en_US unchanged
pgf: left en_US unchanged
ps: left en_US unchanged
svg: left en_US unchanged
template: left en_US unchanged

Output on Linux:

GTK3Agg: changed locale from en_US.utf8 to de_DE.UTF-8
GTK3Cairo: changed locale from en_US.utf8 to de_DE.UTF-8
GTK4Agg: raised ImportError
GTK4Cairo: raised ImportError
MacOSX: raised ImportError
nbAgg: left en_US.utf8 unchanged
QtAgg: changed locale from en_US.utf8 to de_DE.UTF-8
QtCairo: changed locale from en_US.utf8 to de_DE.UTF-8
Qt5Agg: changed locale from en_US.utf8 to de_DE.UTF-8
Qt5Cairo: changed locale from en_US.utf8 to de_DE.UTF-8
TkAgg: changed locale from en_US.utf8 to C
TkCairo: changed locale from en_US.utf8 to C
WebAgg: left en_US.utf8 unchanged
WX: left en_US.utf8 unchanged
WXAgg: left en_US.utf8 unchanged
WXCairo: left en_US.utf8 unchanged
agg: left en_US.utf8 unchanged
cairo: left en_US.utf8 unchanged
pdf: left en_US.utf8 unchanged
pgf: left en_US.utf8 unchanged
ps: left en_US.utf8 unchanged
svg: left en_US.utf8 unchanged
template: left en_US.utf8 unchanged