diff --git a/Lib/curses/textpad.py b/Lib/curses/textpad.py
index 57b2f4a523c95bc..c58a7174d194cf3 100644
--- a/Lib/curses/textpad.py
+++ b/Lib/curses/textpad.py
@@ -56,13 +56,42 @@ def _update_max_yx(self):
         self.maxy = maxy - 1
         self.maxx = maxx - 1
 
+    def _decode(self, ch):
+        # The text of a chtype cell or input byte, decoded with the window's
+        # encoding.  A_CHARTEXT keeps the character byte, dropping the attributes.
+        return bytes([ch & curses.A_CHARTEXT]).decode(self.win.encoding, 'replace')
+
+    def _char_at(self, *yx):
+        # The text of the cell at the given position (default: the cursor).
+        # instr() re-encodes it to the window's encoding; inch() cannot
+        # represent a non-ASCII 8-bit-locale character on a wide build.
+        return self.win.instr(*yx, 1).decode(self.win.encoding, 'replace')
+
+    def _cell_at(self, *yx):
+        # The cell at the given position (default: the cursor) as a chtype
+        # addch() can write back with its rendition.  inch() mangles a non-ASCII
+        # character on a wide build, so take the byte from instr() and the
+        # attributes from inch().
+        return self.win.instr(*yx, 1)[0] | self.win.inch(*yx) & curses.A_ATTRIBUTES
+
+    def _isprint(self, cell):
+        # Whether a chtype cell holds a printable character; _decode() drops the
+        # attribute bits.
+        return self._decode(cell).isprintable()
+
+    def _printable_key(self, ch):
+        # Whether the integer keystroke is a printable character, not a key
+        # code.  0..255 are character bytes (decoded with the window's encoding);
+        # larger values are function and navigation keys.
+        return ch <= 0xff and self._decode(ch).isprintable()
+
     def _end_of_line(self, y):
         """Go to the location of the first blank on the given line,
         returning the index of the last non-blank character."""
         self._update_max_yx()
         last = self.maxx
         while True:
-            if curses.ascii.ascii(self.win.inch(y, last)) != curses.ascii.SP:
+            if self._char_at(y, last) != ' ':
                 last = min(self.maxx, last+1)
                 break
             elif last == 0:
@@ -76,15 +105,16 @@ def _insert_printable_char(self, ch):
         backyx = None
         while True:
             if self.insert_mode:
-                oldch = self.win.inch()
+                oldch = self._cell_at()
             if y >= self.maxy and x >= self.maxx:
                 # Use insch() in the lower-right cell: addch() there would move
                 # the cursor out of the window, raising an error and scrolling
-                # a scrollable window.
-                self.win.insch(ch)
+                # a scrollable window.  Pass it as text: insch() does not decode
+                # an int byte through the locale on a wide build.
+                self.win.insch(self._decode(ch), ch & curses.A_ATTRIBUTES)
                 break
             self.win.addch(ch)
-            if not self.insert_mode or not curses.ascii.isprint(oldch):
+            if not self.insert_mode or not self._isprint(oldch):
                 break
             ch = oldch
             (y, x) = self.win.getyx()
@@ -100,7 +130,7 @@ def do_command(self, ch):
         self._update_max_yx()
         (y, x) = self.win.getyx()
         self.lastcmd = ch
-        if curses.ascii.isprint(ch):
+        if self._printable_key(ch):
             self._insert_printable_char(ch)
         elif ch == curses.ascii.SOH:                           # ^a
             self.win.move(y, 0)
@@ -174,7 +204,7 @@ def gather(self):
             for x in range(self.maxx+1):
                 if self.stripspaces and x > stop:
                     break
-                result = result + chr(curses.ascii.ascii(self.win.inch(y, x)))
+                result = result + self._char_at(y, x)
             if self.maxy > 0:
                 result = result + "\n"
         return result
diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index c17f4c87705c46c..6a6ef6e0226ef62 100644
--- a/Lib/test/test_curses.py
+++ b/Lib/test/test_curses.py
@@ -1993,6 +1993,68 @@ def test_textbox_fill_last_cell_scrollok(self):
         self._type(box, 'def')
         self.assertEqual(box.gather(), 'abc\ndef\n')
 
+    def test_textbox_8bit(self):
+        # A character of an 8-bit locale encoding is entered and read back
+        # through the byte API.  The byte path also runs on a wide build, so the
+        # test is not skipped there.  Run the suite under an 8-bit locale
+        # (ISO-8859-1, ISO-8859-15 or KOI8-U) to reach the non-ASCII cases; each
+        # string is used only if the encoding maps it to single bytes.  'abc' is
+        # ASCII, 'café' is common to the Latin encodings, and the rest are
+        # distinctive (byte 0xA4 is '¤'/'€'/'є' in ISO-8859-1/-15/KOI8-U).
+        encoding = self.stdscr.encoding
+        for text in ['abc', 'café', 'naïve ¤¦', 'café €Šž', 'дякую єі']:
+            try:
+                data = text.encode(encoding)
+            except UnicodeEncodeError:
+                continue
+            if len(data) != len(text):
+                continue       # a multibyte encoding is not the 8-bit byte path
+            with self.subTest(text=text):
+                box, win = self._make_textbox(1, 16)
+                for byte in data:
+                    box.do_command(byte)
+                self.assertEqual(box.gather(), text + ' ')
+
+    def test_textbox_8bit_insert(self):
+        # Insert mode shifts the rest of the line right by reading each cell back
+        # and rewriting it; a non-ASCII 8-bit-locale character must survive the
+        # shift, even on a wide build where inch() mangles it.  See
+        # test_textbox_8bit for the character choices.
+        encoding = self.stdscr.encoding
+        for ch in ['é', '¤', '€', 'є']:
+            try:
+                data = ch.encode(encoding)
+            except UnicodeEncodeError:
+                continue
+            if len(data) != 1:
+                continue
+            with self.subTest(ch=ch):
+                box, win = self._make_textbox(1, 10, insert_mode=True)
+                for byte in ('a' + ch + 'c').encode(encoding):
+                    box.do_command(byte)
+                win.move(0, 1)
+                box.do_command(ord('b'))   # insert 'b', shifting ch and 'c' right
+                self.assertEqual(box.gather(), 'ab' + ch + 'c ')
+
+    def test_textbox_8bit_fill_last_cell(self):
+        # A non-ASCII 8-bit-locale character must survive being written to the
+        # lower-right cell, which uses insch() rather than addch().  See
+        # test_textbox_8bit for the character choices.
+        encoding = self.stdscr.encoding
+        for ch in ['é', '¤', '€', 'є']:
+            try:
+                data = ch.encode(encoding)
+            except UnicodeEncodeError:
+                continue
+            if len(data) != 1:
+                continue
+            with self.subTest(ch=ch):
+                text = 'ab' + ch         # the last character fills the corner
+                box, win = self._make_textbox(1, len(text), stripspaces=0)
+                for byte in text.encode(encoding):
+                    box.do_command(byte)
+                self.assertEqual(box.gather(), text)
+
     def test_textbox_movement(self):
         box, win = self._make_textbox(3, 10)
         self._type(box, 'abc')
@@ -2369,6 +2431,11 @@ def setUp(self):
         self.mock_win = MagicMock(spec=curses.window)
         self.mock_win.getyx.return_value = (1, 1)
         self.mock_win.getmaxyx.return_value = (10, 20)
+        self.mock_win.encoding = 'utf-8'
+        # A non-blank cell so that _end_of_line() reports a full line: instr()
+        # backs the text reads, inch() the insert-mode shift.
+        self.mock_win.instr.return_value = b'x'
+        self.mock_win.inch.return_value = ord('x')
         self.textbox = curses.textpad.Textbox(self.mock_win)
 
     def test_init(self):
diff --git a/Misc/NEWS.d/next/Library/2026-06-27-12-30-00.gh-issue-133031.Na8Bit.rst b/Misc/NEWS.d/next/Library/2026-06-27-12-30-00.gh-issue-133031.Na8Bit.rst
new file mode 100644
index 000000000000000..96e9efe20e42f04
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-27-12-30-00.gh-issue-133031.Na8Bit.rst
@@ -0,0 +1,3 @@
+:class:`curses.textpad.Textbox` now enters and reads back the non-ASCII
+characters of an 8-bit locale encoding, instead of mangling them with a 7-bit
+mask.