matplotlib · QuLogic · Mar 22, 2025 · QuLogic · May 7, 2025 · story645
diff --git a/doc/users/next_whats_new/text_language.rst b/doc/users/next_whats_new/text_language.rst
@@ -0,0 +1,37 @@
+Specifying text language
+------------------------
+
+OpenType fonts may support language systems which can be used to select different
+typographic conventions, e.g., localized variants of letters that share a single Unicode
+code point, or different default font features. The text API now supports setting a
+language to be used and may be set/get with:
+
+- `matplotlib.text.Text.set_language` / `matplotlib.text.Text.get_language`
+- Any API that creates a `.Text` object by passing the *language* argument (e.g.,
+  ``plt.xlabel(..., language=...)``)
+
+The language of the text must be in a format accepted by libraqm, namely `a BCP47
+language code <https://www.w3.org/International/articles/language-tags/>`_. If None or
+unset, then no particular language will be implied, and default font settings will be
+used.
+
+For example, the default font ``DejaVu Sans`` supports language-specific glyphs in the
+Serbian and Macedonian languages in the Cyrillic alphabet, or the Sámi family of
+languages in the Latin alphabet.
+
+.. plot::
+    :include-source:
+
+    fig = plt.figure(figsize=(7, 3))
+
+    char = '\U00000431'
+    fig.text(0.5, 0.8, f'\\U{ord(char):08x}', fontsize=40, horizontalalignment='center')
+    fig.text(0, 0.6, f'Serbian: {char}', fontsize=40, language='sr')
+    fig.text(1, 0.6, f'Russian: {char}', fontsize=40, language='ru',
+             horizontalalignment='right')
+
+    char = '\U0000014a'
+    fig.text(0.5, 0.3, f'\\U{ord(char):08x}', fontsize=40, horizontalalignment='center')
+    fig.text(0, 0.1, f'English: {char}', fontsize=40, language='en')
+    fig.text(1, 0.1, f'Inari Sámi: {char}', fontsize=40, language='smn',
+             horizontalalignment='right')
diff --git a/lib/matplotlib/_text_helpers.py b/lib/matplotlib/_text_helpers.py
@@ -43,7 +43,7 @@ def warn_on_missing_glyph(codepoint, fontnames):
            f"Matplotlib currently does not support {block} natively.")


-def layout(string, font, *, kern_mode=Kerning.DEFAULT):
+def layout(string, font, *, language=None, kern_mode=Kerning.DEFAULT):
    """
    Render *string* with *font*.

@@ -56,6 +56,9 @@ def layout(string, font, *, kern_mode=Kerning.DEFAULT):
        The string to be rendered.
    font : FT2Font
        The font.
+    language : str or list of tuples of (str, int, int), optional
+        The language of the text in a format accepted by libraqm, namely `a BCP47
+        language code <https://www.w3.org/International/articles/language-tags/>`_.
    kern_mode : Kerning
        A FreeType kerning mode.

@@ -65,7 +68,7 @@ def layout(string, font, *, kern_mode=Kerning.DEFAULT):
    """
    x = 0
    prev_glyph_idx = None
-    char_to_font = font._get_fontmap(string)
+    char_to_font = font._get_fontmap(string)  # TODO: Pass in language.
    base_font = font
    for char in string:
        # This has done the fallback logic

diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -189,7 +189,8 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
        font = self._prepare_font(prop)
        # We pass '0' for angle here, since it will be rotated (in raster
        # space) in the following call to draw_text_image).
-        font.set_text(s, 0, flags=get_hinting_flag())
+        font.set_text(s, 0, flags=get_hinting_flag(),
+                      language=mtext.get_language() if mtext is not None else None)
        font.draw_glyphs_to_bitmap(
            antialiased=gc.get_antialiased())
        d = font.get_descent() / 64.0

diff --git a/lib/matplotlib/backends/backend_pdf.py b/lib/matplotlib/backends/backend_pdf.py
@@ -2342,6 +2342,7 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
            return self.draw_mathtext(gc, x, y, s, prop, angle)

        fontsize = prop.get_size_in_points()
+        language = mtext.get_language() if mtext is not None else None

        if mpl.rcParams['pdf.use14corefonts']:
            font = self._get_font_afm(prop)
@@ -2352,7 +2353,7 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
            fonttype = mpl.rcParams['pdf.fonttype']

        if gc.get_url() is not None:
-            font.set_text(s)
+            font.set_text(s, language=language)
            width, height = font.get_width_height()
            self.file._annotations[-1][1].append(_get_link_annotation(
                gc, x, y, width / 64, height / 64, angle))
@@ -2386,7 +2387,8 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
            multibyte_glyphs = []
            prev_was_multibyte = True
            prev_font = font
-            for item in _text_helpers.layout(s, font, kern_mode=Kerning.UNFITTED):
+            for item in _text_helpers.layout(s, font, language=language,
+                                             kern_mode=Kerning.UNFITTED):
                if _font_supports_glyph(fonttype, ord(item.char)):
                    if prev_was_multibyte or item.ft_object != prev_font:
                        singlebyte_chunks.append((item.ft_object, item.x, []))

diff --git a/lib/matplotlib/backends/backend_ps.py b/lib/matplotlib/backends/backend_ps.py
@@ -794,9 +794,10 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
                thisx += width * scale

        else:
+            language = mtext.get_language() if mtext is not None else None
            font = self._get_font_ttf(prop)
            self._character_tracker.track(font, s)
-            for item in _text_helpers.layout(s, font):
+            for item in _text_helpers.layout(s, font, language=language):
                ps_name = (item.ft_object.postscript_name
                           .encode("ascii", "replace").decode("ascii"))
                glyph_name = item.ft_object.get_glyph_name(item.glyph_idx)

diff --git a/lib/matplotlib/ft2font.pyi b/lib/matplotlib/ft2font.pyi
@@ -236,7 +236,12 @@ class FT2Font(Buffer):
    def set_charmap(self, i: int) -> None: ...
    def set_size(self, ptsize: float, dpi: float) -> None: ...
    def set_text(
-        self, string: str, angle: float = ..., flags: LoadFlags = ...
+        self,
+        string: str,
+        angle: float = ...,
+        flags: LoadFlags = ...,
+        *,
+        language: str | list[tuple[str, int, int]] | None = ...,
    ) -> NDArray[np.float64]: ...
    @property
    def ascender(self) -> int: ...

diff --git a/lib/matplotlib/mpl-data/matplotlibrc b/lib/matplotlib/mpl-data/matplotlibrc
@@ -292,6 +292,11 @@
 ## for more information on text properties
 #text.color: black

+## The language of the text in a format accepted by libraqm, namely `a BCP47 language
+## code <https://www.w3.org/International/articles/language-tags/>`_. If None, then no
+## particular language will be implied, and default font settings will be used.
+#text.language: None
+
 ## FreeType hinting flag ("foo" corresponds to FT_LOAD_FOO); may be one of the
 ## following (Proprietary Matplotlib-specific synonyms are given in parentheses,
 ## but their use is discouraged):

diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -1032,6 +1032,7 @@ def _convert_validator_spec(key, conv):
    "text.kerning_factor": validate_int,
    "text.antialiased":    validate_bool,
    "text.parse_math":     validate_bool,
+    "text.language":       validate_string_or_None,

    "mathtext.cal":            validate_font_properties,
    "mathtext.rm":             validate_font_properties,

diff --git a/lib/matplotlib/tests/test_ft2font.py b/lib/matplotlib/tests/test_ft2font.py
@@ -775,6 +775,37 @@ def test_ft2font_set_text():
    assert font.get_bitmap_offset() == (6, 0)


+@pytest.mark.parametrize(
+    'input',
+    [
+        [1, 2, 3],
+        [(1, 2)],
+        [('en', 'foo', 2)],
+        [('en', 1, 'foo')],
+    ],
+    ids=[
+        'nontuple',
+        'wrong length',
+        'wrong start type',
+        'wrong end type',
+    ],
+)
+def test_ft2font_language_invalid(input):
+    file = fm.findfont('DejaVu Sans')
+    font = ft2font.FT2Font(file, hinting_factor=1, _kerning_factor=0)
+    with pytest.raises(TypeError):
+        font.set_text('foo', language=input)
+
+
+def test_ft2font_language():
+    # TODO: This is just a smoke test.
+    file = fm.findfont('DejaVu Sans')
+    font = ft2font.FT2Font(file, hinting_factor=1, _kerning_factor=0)
+    font.set_text('foo')
+    font.set_text('foo', language='en')
+    font.set_text('foo', language=[('en', 1, 2)])
+
+
 def test_ft2font_loading():
    file = fm.findfont('DejaVu Sans')
    font = ft2font.FT2Font(file, hinting_factor=1, _kerning_factor=0)

diff --git a/lib/matplotlib/tests/test_text.py b/lib/matplotlib/tests/test_text.py
@@ -1199,3 +1199,24 @@ def test_ytick_rotation_mode():
        tick.set_rotation(angle)

    plt.subplots_adjust(left=0.4, right=0.6, top=.99, bottom=.01)
+
+
+@pytest.mark.parametrize(
+    'input, match',
+    [
+        ([1, 2, 3], 'must be list of tuple'),
+        ([(1, 2)], 'must be list of tuple'),
+        ([('en', 'foo', 2)], 'start location must be int'),
+        ([('en', 1, 'foo')], 'end location must be int'),
+    ],
+)
+def test_text_language_invalid(input, match):
+    with pytest.raises(TypeError, match=match):
+        Text(0, 0, 'foo', language=input)
+
+
+def test_text_language():
+    # TODO: This is just a smoke test.
+    Text(0, 0, 'foo', language='en')
+    Text(0, 0, 'foo', language=[('en', 1, 2)])
+    Text(0, 0, 'foo', language=(('en', 1, 2), ))  # Not documented, but we'll allow it.
diff --git a/lib/matplotlib/text.py b/lib/matplotlib/text.py
@@ -136,6 +136,7 @@
        super().__init__()
        self._x, self._y = x, y
        self._text = ''
+        self._language = None
        self._reset_visual_defaults(
            text=text,
            color=color,
@@ -1422,6 +1423,41 @@
            return 'baseline' if anchor_at_left else 'top'
        return 'top' if anchor_at_left else 'baseline'

+    def get_language(self):
+        """Return the language this Text is in."""
+        return self._language
+
+    def set_language(self, language):
+        """
+        Set the language of the text.
+
+        Parameters
+        ----------
+        language : str or list[tuple[str, int, int]] or None
+            The language of the text in a format accepted by libraqm, namely `a BCP47
+            language code <https://www.w3.org/International/articles/language-tags/>`_.
+
+            If None, then defaults to :rc:`text.language`.
+        """
+        _api.check_isinstance((list, tuple, str, None), language=language)
+        language = mpl._val_or_rc(language, 'text.language')
+
+        if not cbook.is_scalar_or_string(language):
+            for val in language:
+                if not isinstance(val, tuple) or len(val) != 3:
+                    raise TypeError('language must be list of tuple, not {language!r}')
+                sublang, start, end = val
+                if not isinstance(sublang, str):
+                    raise TypeError(
+                        'sub-language specification must be str, not {sublang!r}')
+                if not isinstance(start, int):
+                    raise TypeError('start location must be int, not {start!r}')
+                if not isinstance(end, int):
+                    raise TypeError('end location must be int, not {end!r}')
+
+        self._language = language
+        self.stale = True
+

 class OffsetFrom:
    """Callable helper class for working with `Annotation`."""

diff --git a/lib/matplotlib/text.pyi b/lib/matplotlib/text.pyi
@@ -108,6 +108,8 @@ class Text(Artist):
    def set_antialiased(self, antialiased: bool) -> None: ...
    def _ha_for_angle(self, angle: Any) -> Literal['center', 'right', 'left'] | None: ...
    def _va_for_angle(self, angle: Any) -> Literal['center', 'top', 'baseline'] | None: ...
+    def get_language(self) -> str | list[tuple[str, int, int]] | None: ...
+    def set_language(self, language: str | list[tuple[str, int, int]] | None) -> None: ...

 class OffsetFrom:
    def __init__(

diff --git a/lib/matplotlib/textpath.py b/lib/matplotlib/textpath.py
@@ -69,7 +69,7 @@ def get_text_width_height_descent(self, s, prop, ismath):
        d /= 64.0
        return w * scale, h * scale, d * scale

-    def get_text_path(self, prop, s, ismath=False):
+    def get_text_path(self, prop, s, ismath=False, *, language=None):
        """
        Convert text *s* to path (a tuple of vertices and codes for
        matplotlib.path.Path).
@@ -82,6 +82,9 @@ def get_text_path(self, prop, s, ismath=False):
            The text to be converted.
        ismath : {False, True, "TeX"}
            If True, use mathtext parser.  If "TeX", use tex for rendering.
+        language : str or list of tuples of (str, int, int), optional
+            The language of the text in a format accepted by libraqm, namely `a BCP47
+            language code <https://www.w3.org/International/articles/language-tags/>`_.

        Returns
        -------
@@ -109,7 +112,8 @@ def get_text_path(self, prop, s, ismath=False):
            glyph_info, glyph_map, rects = self.get_glyphs_tex(prop, s)
        elif not ismath:
            font = self._get_font(prop)
-            glyph_info, glyph_map, rects = self.get_glyphs_with_font(font, s)
+            glyph_info, glyph_map, rects = self.get_glyphs_with_font(font, s,
+                                                                     language=language)
        else:
            glyph_info, glyph_map, rects = self.get_glyphs_mathtext(prop, s)

@@ -130,7 +134,7 @@ def get_text_path(self, prop, s, ismath=False):
        return verts, codes

    def get_glyphs_with_font(self, font, s, glyph_map=None,
-                             return_new_glyphs_only=False):
+                             return_new_glyphs_only=False, *, language=None):
        """
        Convert string *s* to vertices and codes using the provided ttf font.
        """
@@ -145,7 +149,7 @@ def get_glyphs_with_font(self, font, s, glyph_map=None,

        xpositions = []
        glyph_ids = []
-        for item in _text_helpers.layout(s, font):
+        for item in _text_helpers.layout(s, font, language=language):
            char_id = self._get_char_id(item.ft_object, ord(item.char))
            glyph_ids.append(char_id)
            xpositions.append(item.x)

diff --git a/lib/matplotlib/textpath.pyi b/lib/matplotlib/textpath.pyi
@@ -16,14 +16,17 @@ class TextToPath:
        self, s: str, prop: FontProperties, ismath: bool | Literal["TeX"]
    ) -> tuple[float, float, float]: ...
    def get_text_path(
-        self, prop: FontProperties, s: str, ismath: bool | Literal["TeX"] = ...
+        self, prop: FontProperties, s: str, ismath: bool | Literal["TeX"] = ..., *,
+        language: str | list[tuple[str, int, int]] | None = ...,
    ) -> list[np.ndarray]: ...
    def get_glyphs_with_font(
        self,
        font: FT2Font,
        s: str,
        glyph_map: dict[str, tuple[np.ndarray, np.ndarray]] | None = ...,
        return_new_glyphs_only: bool = ...,
+        *,
+        language: str | list[tuple[str, int, int]] | None = ...,
    ) -> tuple[
        list[tuple[str, float, float, float]],
        dict[str, tuple[np.ndarray, np.ndarray]],

diff --git a/src/ft2font.cpp b/src/ft2font.cpp
@@ -309,7 +309,9 @@ void FT2Font::set_kerning_factor(int factor)
 }

 void FT2Font::set_text(
-    std::u32string_view text, double angle, FT_Int32 flags, std::vector<double> &xys)
+    // TODO: languages is unused with FreeType, but will with libraqm.
+    std::u32string_view text, double angle, FT_Int32 flags, LanguageType languages,
+    std::vector<double> &xys)
 {
    FT_Matrix matrix; /* transformation matrix */


diff --git a/src/ft2font.h b/src/ft2font.h
@@ -6,6 +6,7 @@
 #ifndef MPL_FT2FONT_H
 #define MPL_FT2FONT_H

+#include <optional>
 #include <set>
 #include <string>
 #include <string_view>
@@ -98,6 +99,9 @@ class FT2Font
    typedef void (*WarnFunc)(FT_ULong charcode, std::set<FT_String*> family_names);

  public:
+    using LanguageRange = std::tuple<std::string, int, int>;
+    using LanguageType = std::optional<std::vector<LanguageRange>>;
+
    FT2Font(FT_Open_Args &open_args, long hinting_factor,
            std::vector<FT2Font *> &fallback_list,
            WarnFunc warn, bool warn_if_used);
@@ -107,7 +111,7 @@ class FT2Font
    void set_charmap(int i);
    void select_charmap(unsigned long i);
    void set_text(std::u32string_view codepoints, double angle, FT_Int32 flags,
-                  std::vector<double> &xys);
+                  LanguageType languages, std::vector<double> &xys);
    int get_kerning(FT_UInt left, FT_UInt right, FT_Kerning_Mode mode);
    void set_kerning_factor(int factor);
    void load_char(long charcode, FT_Int32 flags, FT2Font *&ft_object, bool fallback);