timhoffm · Oct 22, 2026 · Sep 10, 2026 · Oct 21, 2026
diff --git a/doc/api/next_api_changes/behavior/32281-CAZM.rst b/doc/api/next_api_changes/behavior/32281-CAZM.rst
@@ -0,0 +1,9 @@
+``EngFormatter.format_data`` honors ``axes.unicode_minus``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`.EngFormatter.format_data` and `.EngFormatter.format_eng` now honor
+:rc:`axes.unicode_minus`, like `.ScalarFormatter.format_data`. With the default
+rcParams, negative values are returned with a Unicode minus sign (U+2212)
+instead of an ASCII hyphen (U+002D), as are negative exponents of values beyond
+the range of SI prefixes. Tick labels and the offset text already used
+the Unicode minus, so plots are unchanged.
diff --git a/doc/release/next_whats_new/engformatter_locale.rst b/doc/release/next_whats_new/engformatter_locale.rst
@@ -0,0 +1,17 @@
+``EngFormatter`` now respects ``axes.formatter.use_locale``
+-----------------------------------------------------------
+
+`~matplotlib.ticker.EngFormatter` now formats the decimal separator according to
+the current locale, like `~matplotlib.ticker.ScalarFormatter` already did. This
+is controlled by the :rc:`axes.formatter.use_locale` rcParam, or by the new
+*useLocale* keyword argument:
+
+.. code-block:: python
+
+    import locale
+    from matplotlib.ticker import EngFormatter
+
+    locale.setlocale(locale.LC_ALL, "de_DE.UTF-8")
+
+    ax.yaxis.set_major_formatter(EngFormatter(places=2, useLocale=True))
+    # tick labels now read "555,10 m" instead of "555.10 m"
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -1571,6 +1571,7 @@ def test_params(self, unicode_minus, input, expected):
         )
         for _formatter, _exp_output in zip(formatters, exp_outputs):
             assert _formatter(input) == _exp_output
+            assert _formatter.format_data(input) == _exp_output
 
         # Case 1: unit=UNIT and sep=' ' (default).
         # Append a unit symbol to the reference case.
@@ -1810,6 +1811,45 @@ def test_locale_comma():
         pytest.skip(skip_msg)
 
 
+def _impl_engformatter_locale():
+    try:
+        locale.setlocale(locale.LC_ALL, 'de_DE.UTF-8')
+    except locale.Error:
+        print('SKIP: Locale de_DE.UTF-8 is not supported on this machine')
+        return
+    # EngFormatter is a ScalarFormatter subclass, so it must honour the
+    # axes.formatter.use_locale rcParam like its parent does.
+    with mpl.rc_context(rc={'axes.formatter.use_locale': True}):
+        fmt = mticker.EngFormatter(places=2)
+        assert fmt.get_useLocale()
+        assert fmt.format_data(0.5551) == '555,10 m'
+        # An explicit keyword argument overrides the rcParam.
+        fmt = mticker.EngFormatter(places=2, useLocale=False)
+        assert not fmt.get_useLocale()
+        assert fmt.format_data(1234.5) == '1.23 k'
+    fmt = mticker.EngFormatter(places=2, useLocale=True)
+    assert fmt.get_useLocale()
+    assert fmt.format_data(1234.5) == '1,23 k'
+    # The inherited setter also reaches the engineering formatting path.
+    fmt = mticker.EngFormatter(places=2, useLocale=False)
+    fmt.set_useLocale(True)
+    assert fmt.format_data(1234.5) == '1,23 k'
+    # Separators are escaped for mathtext, as ScalarFormatter does.
+    fmt = mticker.EngFormatter(places=2, useLocale=True, useMathText=True)
+    assert fmt.format_data(0.5551) == '$555{,}10$ m'
+
+
+def test_engformatter_locale():
+    proc = mpl.testing.subprocess_run_helper(
+        _impl_engformatter_locale, timeout=60, extra_env={'MPLBACKEND': 'Agg'})
+    skip_msg = next((line[len('SKIP:'):].strip()
+                     for line in proc.stdout.splitlines()
+                     if line.startswith('SKIP:')),
+                    '')
+    if skip_msg:
+        pytest.skip(skip_msg)
+
+
 def test_majformatter_type():
     fig, ax = plt.subplots()
     with pytest.raises(TypeError):

diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -1433,7 +1433,7 @@ class EngFormatter(ScalarFormatter):
     }
 
     def __init__(self, unit="", places=None, sep=" ", *, usetex=None,
-                 useMathText=None, useOffset=False):
+                 useMathText=None, useOffset=False, useLocale=None):
         r"""
         Parameters
         ----------
@@ -1476,14 +1476,20 @@ def __init__(self, unit="", places=None, sep=" ", *, usetex=None,
             3 digits. See also `.set_useOffset`.
 
             .. versionadded:: 3.10
+
+        useLocale : bool, default: :rc:`axes.formatter.use_locale`.
+            Whether to use locale settings for decimal sign and positive sign.
+            See `.set_useLocale`.
+
+            .. versionadded:: 3.12
         """
         self.unit = unit
         self.places = places
         self.sep = sep
         super().__init__(
             useOffset=useOffset,
             useMathText=useMathText,
-            useLocale=False,
+            useLocale=useLocale,
             usetex=usetex,
         )
 
@@ -1564,7 +1570,10 @@ def format_data(self, value):
         '1.0 M'
 
         >>> format_data(-1e-6)  # for self.places = 2
-        '-1.00 \N{MICRO SIGN}'
+        '\N{MINUS SIGN}1.00 \N{MICRO SIGN}'
+
+        .. versionchanged:: 3.12
+           The result now honors :rc:`axes.unicode_minus`.
         """
         sign = 1
         fmt = "g" if self.places is None else f".{self.places:d}f"
@@ -1598,10 +1607,11 @@ def format_data(self, value):
             suffix = f"{self.sep}{unit_prefix}{self.unit}"
         else:
             suffix = ""
+        mant_str = self._format_maybe_minus_and_locale(f"%{fmt}", mant)
         if self._usetex or self._useMathText:
-            return f"${mant:{fmt}}${suffix}"
+            return f"${mant_str}${suffix}"
         else:
-            return f"{mant:{fmt}}{suffix}"
+            return f"{mant_str}{suffix}"
 
 
 class PercentFormatter(Formatter):

diff --git a/lib/matplotlib/ticker.pyi b/lib/matplotlib/ticker.pyi
@@ -150,6 +150,7 @@ class EngFormatter(ScalarFormatter):
         usetex: bool | None = ...,
         useMathText: bool | None = ...,
         useOffset: bool | float | None = ...,
+        useLocale: bool | None = ...,
     ) -> None: ...
     def format_eng(self, num: float) -> str: ...