diff --git a/src/specify_cli/__init__.py b/src/specify_cli/__init__.py
index c0bdbaabe3..559e6df5f8 100644
--- a/src/specify_cli/__init__.py
+++ b/src/specify_cli/__init__.py
@@ -397,7 +397,15 @@ def save_init_options(project_path: Path, options: dict[str, Any]) -> None:
     """
     dest = project_path / INIT_OPTIONS_FILE
     dest.parent.mkdir(parents=True, exist_ok=True)
-    dest.write_text(json.dumps(options, indent=2, sort_keys=True))
+    # Pin UTF-8 explicitly: ``Path.write_text`` defaults to the system
+    # locale codec, which is cp1252 / gb2312 / cp932 on Windows. A
+    # locale-encoded write succeeds locally but produces a file a peer
+    # machine (different locale) or Unix CI cannot decode. The sibling
+    # integration-catalog writer in ``integrations/catalog.py`` already
+    # pins ``encoding="utf-8"`` for the same reason.
+    dest.write_text(
+        json.dumps(options, indent=2, sort_keys=True), encoding="utf-8"
+    )
 
 
 def load_init_options(project_path: Path) -> dict[str, Any]:
@@ -409,8 +417,15 @@ def load_init_options(project_path: Path) -> dict[str, Any]:
     if not path.exists():
         return {}
     try:
-        return json.loads(path.read_text())
-    except (json.JSONDecodeError, OSError):
+        # Match the explicit UTF-8 used by ``save_init_options``; without
+        # it ``read_text`` falls back to the system codec on Windows and
+        # raises ``UnicodeDecodeError`` on any file a peer wrote with
+        # non-ASCII content. ``UnicodeDecodeError`` is a subclass of
+        # ``ValueError``, not ``OSError`` / ``json.JSONDecodeError``, so
+        # it must be listed explicitly here to preserve the existing
+        # "fall back to empty dict" contract.
+        return json.loads(path.read_text(encoding="utf-8"))
+    except (json.JSONDecodeError, OSError, UnicodeDecodeError):
         return {}
 
 
diff --git a/src/specify_cli/extensions.py b/src/specify_cli/extensions.py
index 871503f0ae..ba8020279b 100644
--- a/src/specify_cli/extensions.py
+++ b/src/specify_cli/extensions.py
@@ -761,7 +761,13 @@ def _load_extensionignore(source_dir: Path) -> Optional[Callable[[str, List[str]
         if not ignore_file.exists():
             return None
 
-        lines: List[str] = ignore_file.read_text().splitlines()
+        # Pin UTF-8 explicitly: ``Path.read_text`` defaults to the system
+        # locale codec on Windows (cp1252 / gb2312 / cp932), which silently
+        # corrupts multibyte patterns when the file is shared across
+        # machines with different locales. The next line already
+        # normalises backslashes "so Windows-authored files work" — the
+        # codebase already expects Windows authors to write this file.
+        lines: List[str] = ignore_file.read_text(encoding="utf-8").splitlines()
 
         # Normalise backslashes in patterns so Windows-authored files work
         normalised: List[str] = []
diff --git a/tests/test_extensions.py b/tests/test_extensions.py
index 153388a541..9cdf7b3ea2 100644
--- a/tests/test_extensions.py
+++ b/tests/test_extensions.py
@@ -3147,9 +3147,13 @@ def _make_extension(self, temp_dir, valid_manifest_data, extra_files=None, ignor
                 else:
                     p.write_text(content)
 
-        # Write .extensionignore
+        # Write .extensionignore. Pinned to UTF-8 so non-ASCII patterns
+        # in tests (see ``test_extensionignore_utf8_patterns``) survive
+        # the round-trip on Windows runners with non-UTF-8 default locales.
         if ignore_content is not None:
-            (ext_dir / ".extensionignore").write_text(ignore_content)
+            (ext_dir / ".extensionignore").write_text(
+                ignore_content, encoding="utf-8"
+            )
 
         return ext_dir
 
@@ -3379,6 +3383,44 @@ def test_extensionignore_windows_backslash_patterns(self, temp_dir, valid_manife
         assert (dest / "docs" / "guide.md").exists()
         assert not (dest / "docs" / "internal" / "draft.md").exists()
 
+    def test_extensionignore_utf8_patterns(self, temp_dir, valid_manifest_data):
+        """Non-ASCII patterns in .extensionignore work on every locale.
+
+        ``Path.read_text`` defaults to the system locale codec on Windows
+        (cp1252 / gb2312 / cp932). Without an explicit ``encoding="utf-8"``,
+        a pattern like ``ドキュメント/`` written by a UTF-8 host becomes
+        mojibake on a cp1252 host and silently fails to match — leaking
+        files the author intended to exclude. The existing
+        ``test_extensionignore_windows_backslash_patterns`` already shows
+        the codebase treats this as a Windows-author-friendly file; UTF-8
+        is part of that same contract.
+        """
+        ext_dir = self._make_extension(
+            temp_dir,
+            valid_manifest_data,
+            extra_files={
+                "ドキュメント/private.md": "secret",
+                "ドキュメント/public.md": "public",
+                "docs/guide.md": "# Guide",
+                "café/résumé.txt": "draft",
+            },
+            ignore_content="ドキュメント/\ncafé/\n",
+        )
+
+        proj_dir = temp_dir / "project"
+        proj_dir.mkdir()
+        (proj_dir / ".specify").mkdir()
+
+        manager = ExtensionManager(proj_dir)
+        manager.install_from_directory(ext_dir, "0.1.0", register_commands=False)
+
+        dest = proj_dir / ".specify" / "extensions" / "test-ext"
+        # Multibyte patterns excluded.
+        assert not (dest / "ドキュメント").exists()
+        assert not (dest / "café").exists()
+        # ASCII path with no matching pattern is unaffected.
+        assert (dest / "docs" / "guide.md").exists()
+
     def test_extensionignore_star_does_not_cross_directories(self, temp_dir, valid_manifest_data):
         """'*' should NOT match across directory boundaries (gitignore semantics)."""
         ext_dir = self._make_extension(
diff --git a/tests/test_presets.py b/tests/test_presets.py
index f1c0e95f4e..d3d61b4c5a 100644
--- a/tests/test_presets.py
+++ b/tests/test_presets.py
@@ -2269,6 +2269,45 @@ def test_load_returns_empty_on_invalid_json(self, project_dir):
 
         assert load_init_options(project_dir) == {}
 
+    @pytest.mark.parametrize(
+        "value",
+        ["名前-プロジェクト", "café-résumé", "Ωmega-Δelta", "🚀-launch"],
+    )
+    def test_save_load_round_trip_preserves_non_ascii(self, project_dir, value):
+        """Non-ASCII values round-trip via explicit UTF-8 encoding.
+
+        ``Path.write_text`` / ``Path.read_text`` default to the system
+        locale codec on Windows (cp1252 / gb2312 / cp932). Without
+        ``encoding="utf-8"`` pinned on both ends, a project name like
+        ``café`` written on a UTF-8 host becomes garbled or unreadable on
+        a cp1252 host (and vice versa). Pin UTF-8 explicitly so init
+        options round-trip across machines and CI.
+        """
+        from specify_cli import save_init_options, load_init_options
+
+        save_init_options(project_dir, {"ai": "claude", "project_name": value})
+
+        loaded = load_init_options(project_dir)
+        assert loaded["project_name"] == value
+
+    def test_load_returns_empty_on_locale_corrupted_file(self, project_dir):
+        """A file written in a non-UTF-8 codec falls back to {}, not crash.
+
+        Simulates a file produced by an old client (or by a peer machine
+        with a different default locale) that contains bytes invalid as
+        UTF-8. ``load_init_options`` should fall back to ``{}`` per the
+        existing contract — never propagate a raw ``UnicodeDecodeError``
+        to the CLI surface.
+        """
+        from specify_cli import load_init_options
+
+        opts_file = project_dir / ".specify" / "init-options.json"
+        opts_file.parent.mkdir(parents=True, exist_ok=True)
+        # 0xE9 is 'é' in cp1252 but an invalid lead byte in UTF-8.
+        opts_file.write_bytes(b'{"project_name": "caf\xe9"}')
+
+        assert load_init_options(project_dir) == {}
+
 
 class TestPresetSkills:
     """Tests for preset skill registration and unregistration.