diff --git a/doc/source/_ext/viewer_directive_fix.py b/doc/source/_ext/viewer_directive_fix.py
new file mode 100644
index 000000000..253302608
--- /dev/null
+++ b/doc/source/_ext/viewer_directive_fix.py
@@ -0,0 +1,111 @@
+"""Fix for offlineviewer directive to support nested output directories.
+
+When using atsphinx-mini18n with ``mini18n_build_style = "nested"``, the Japanese
+sub-build outputs to ``build/mini18n-html/ja/``. The upstream
+``pyvista.ext.viewer_directive`` computes the build root as ``outdir.parent``, which
+gives ``build/mini18n-html/`` instead of the correct ``build/``.  This causes the
+``is_path_relative_to`` check to fail and the directive to return an empty node list,
+leaving the "Interactive Scene" tab empty.
+
+The fix: derive the build root from ``doctreedir.parent`` instead of ``outdir.parent``.
+Both the English and Japanese mini18n builds share the same ``doctreedir``
+(``build/.doctrees``), so ``doctreedir.parent = build/`` is correct for both.
+"""
+
+from __future__ import annotations
+
+import os
+import shutil
+from pathlib import Path
+
+from docutils import nodes
+from docutils.parsers.rst import Directive
+from docutils.utils import relative_path  # pragma: no cover
+from sphinx.util import logging
+from trame_vtk.tools.vtksz2html import HTML_VIEWER_PATH
+
+logger = logging.getLogger(__name__)
+
+
+def _is_path_relative_to(path: Path, other: Path) -> bool:
+    return path.is_relative_to(other)
+
+
+class FixedOfflineViewerDirective:
+    """Replacement for OfflineViewerDirective with corrected build-root detection."""
+
+    required_arguments = 1
+    optional_arguments = 0
+    final_argument_whitespace = True
+    has_content = True
+
+    def run(self):  # pragma: no cover
+        source_dir = Path(self.state.document.settings.env.app.srcdir)
+        output_dir = Path(self.state.document.settings.env.app.outdir)
+        # Use doctreedir.parent as the build root so that nested output directories
+        # (e.g., build/mini18n-html/ja/ produced by atsphinx-mini18n) resolve
+        # correctly.  Both the primary and language sub-builds share the same
+        # doctreedir (build/.doctrees), so doctreedir.parent == build/ in all cases.
+        build_dir = Path(self.state.document.settings.env.app.doctreedir).parent
+
+        # path passed to ``.. offlineviewer:: <path>``
+        source_file = str(Path(self.state.document.current_source).parent / self.arguments[0])
+        source_file = Path(source_file).absolute().resolve()
+        if not source_file.is_file():
+            logger.warning("Source file %s does not exist.", source_file)
+            return []
+
+        # copy viewer HTML to _static
+        static_path = output_dir / "_static"
+        static_path.mkdir(exist_ok=True)
+        viewer_name = Path(HTML_VIEWER_PATH).name
+        if not (static_path / viewer_name).exists():
+            shutil.copy(HTML_VIEWER_PATH, static_path)
+
+        if _is_path_relative_to(source_file, build_dir):
+            dest_partial_path = source_file.parent.relative_to(build_dir)
+        elif _is_path_relative_to(source_file, source_dir):
+            dest_partial_path = source_file.parent.relative_to(source_dir)
+        else:
+            logger.warning(
+                "Source file %s is not a subpath of either the build "
+                "directory or the source directory. Cannot extract base path.",
+                source_file,
+            )
+            return []
+
+        dest_path = output_dir / "_images" / dest_partial_path
+        dest_path.mkdir(parents=True, exist_ok=True)
+        dest_file = (dest_path / source_file.name).resolve()
+        if source_file != dest_file:
+            try:
+                shutil.copy(source_file, dest_file)
+            except Exception as e:  # noqa: BLE001
+                logger.warning("Failed to copy file from %s to %s: %s", source_file, dest_file, e)
+
+        relpath_to_source_root = relative_path(self.state.document.current_source, source_dir)
+        rel_viewer_path = (Path() / relpath_to_source_root / "_static" / viewer_name).as_posix()
+        rel_asset_path = Path(os.path.relpath(dest_file, static_path)).as_posix()
+        html = (
+            f"<iframe src='{rel_viewer_path}?fileURL={rel_asset_path}' "
+            "width='100%%' height='400px' frameborder='0'></iframe>"
+        )
+        return [nodes.raw("", html, format="html")]
+
+
+_fixed_directive_class = type(
+    "OfflineViewerDirective",
+    (FixedOfflineViewerDirective, Directive),
+    {},
+)
+
+
+def setup(app):
+    """Re-register the offlineviewer directive with the fixed implementation."""
+    app.add_directive("offlineviewer", _fixed_directive_class, override=True)
+
+    return {
+        "version": "0.1",
+        "parallel_read_safe": True,
+        "parallel_write_safe": True,
+    }
diff --git a/doc/source/conf.py b/doc/source/conf.py
index c90dd29ee..20bb77463 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -10,6 +10,7 @@
 faulthandler.enable()
 
 sys.path.insert(0, str(Path(__file__).absolute().parent))
+sys.path.insert(0, str(Path(__file__).absolute().parent / "_ext"))
 import make_external_gallery  # noqa: E402
 
 make_external_gallery.make_example_gallery()
@@ -58,6 +59,7 @@
     "jupyter_sphinx",
     "pyvista.ext.plot_directive",
     "pyvista.ext.viewer_directive",
+    "viewer_directive_fix",
     "sphinx.ext.autodoc",
     "sphinx.ext.intersphinx",
     "sphinx.ext.napoleon",