Error in code: No filter named 'json'.

In the template there is attempt to use filter called json, which doesn't exist.

TemplateAssertionError: No filter named 'json'.
(9 additional frame(s) were not displayed)
...
  File "jinja2/environment.py", line 969, in _load_template
    template = self.loader.load(self, name, self.make_globals(globals))
  File "jinja2/loaders.py", line 138, in load
    code = environment.compile(source, name, filename)
  File "jinja2/environment.py", line 768, in compile
    self.handle_exception(source=source_hint)
  File "jinja2/environment.py", line 936, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "/app/src/tjts5901/templates/items/update.html", line 31, in template
    <button name="action" form="delete-form" value="delete" class="btn btn-danger" onclick="return confirm({{ _("Are you sure?")|json }});">{{ _("Delete") }}</button>