Fix unintended space after comma as a decimal separator

Author: devRD

lib/matplotlib/tests/test_ticker.py

@@ -1449,6 +1449,21 @@ def test_latex(self, is_latex, usetex, expected):
             assert fmt.format_pct(50, 100) == expected
 
 
+def test_locale_comma():
+    import locale
+
+    currentLocale = locale.getlocale()
+    try:
+        locale.setlocale(locale.LC_ALL, 'fy_DE.UTF-8')
+    except locale.Error as err:
+        pytest.fail("Locale 'fy_DE.UTF-8' is not supported")
+    ticks = mticker.ScalarFormatter(useMathText=True, useLocale=True)
+    fmt = '$\\mathdefault{%1.1f}$'
+    x = ticks._format_maybe_minus_and_locale(fmt, 0.5)
+    locale.setlocale(locale.LC_ALL, currentLocale)
+    assert x == '$\\mathdefault{0{,}5}$'
+
+
 def test_majformatter_type():
     fig, ax = plt.subplots()
     with pytest.raises(TypeError):

lib/matplotlib/ticker.py

@@ -510,8 +510,14 @@ def _format_maybe_minus_and_locale(self, fmt, arg):
         """
         Format *arg* with *fmt*, applying Unicode minus and locale if desired.
         """
-        return self.fix_minus(locale.format_string(fmt, (arg,), True)
-                              if self._useLocale else fmt % arg)
+        return self.fix_minus(
+                # Escape commas introduced by format_string but not those present
+                # from the beginning in fmt.
+                ",".join(locale.format_string(part, (arg,), True)
+                         .replace(",", "{,}")
+                         for part in fmt.split(","))
+                if self._useLocale
+                else fmt % arg)
 
     def get_useMathText(self):
         """