How to use the aeidon.i18n._ function in aeidon

def _show_encoding_error_dialog(self):
        """Show an error dialog after failing to encode file."""
        title = _('Failed to encode subtitle file to temporary directory "{}"').format(tempfile.gettempdir())
        message = _("Subtitle data could not be encoded to a temporary file for preview with the current character encoding. Please first save the subtitle file with a different character encoding.")
        dialog = gaupol.ErrorDialog(self.window, title, message)
        dialog.add_button(_("_OK"), Gtk.ResponseType.OK)
        dialog.set_default_response(Gtk.ResponseType.OK)
        gaupol.util.flash_dialog(dialog)

def __init__(self):
        """Initialize a :class:`ShowHelpMenuAction` instance."""
        gaupol.TopMenuAction.__init__(self, "show_help_menu")
        self.set_label(_("_Help"))
        self.action_group = "main-safe"

def set_framerate(self, framerate, register=-1):
        """Set the value of framerate."""
        orig_framerate = self.framerate
        self.framerate = framerate
        self.calc = aeidon.Calculator(framerate)
        for subtitle in self.subtitles:
            subtitle.framerate = framerate
        action = aeidon.RevertableAction(register=register)
        action.docs = tuple(aeidon.documents)
        action.description = _("Setting framerate")
        action.revert_function = self.set_framerate
        action.revert_args = (orig_framerate,)
        self.register_action(action)

def _show_translation_warning_dialog(self, page):
        """Show a warning dialog if opening a new translation file."""
        title = _('Save changes to translation document "{}" before opening a new one?').format(page.get_translation_basename())
        message = _("If you don't save, changes will be permanently lost.")
        dialog = gaupol.WarningDialog(self.window, title, message)
        dialog.add_button(_("Open _Without Saving"), Gtk.ResponseType.NO)
        dialog.add_button(_("_Cancel"), Gtk.ResponseType.CANCEL)
        dialog.add_button(_("_Save"), Gtk.ResponseType.YES)
        dialog.set_default_response(Gtk.ResponseType.YES)
        response = gaupol.util.flash_dialog(dialog)
        if response == Gtk.ResponseType.YES:
            return self.save_translation(page)
        gaupol.util.raise_default(response != Gtk.ResponseType.NO)

label=_("Seek _Previous"), icon_name="media-skip-backward")
        button.set_action_name("win.seek-previous")
        button.set_tooltip_text(_("Seek to the start of the previous subtitle"))
        self.player_toolbar.insert(button, -1)
        # win.seek-next
        button = Gtk.ToolButton(
            label=_("Seek _Next"), icon_name="media-skip-forward")
        button.set_action_name("win.seek-next")
        button.set_tooltip_text(_("Seek to the start of the next subtitle"))
        self.player_toolbar.insert(button, -1)
        self.player_toolbar.insert(Gtk.SeparatorToolItem(), -1)
        # win.seek-backward
        button = Gtk.ToolButton(
            label=_("Seek _Backward"), icon_name="media-seek-backward")
        button.set_action_name("win.seek-backward")
        button.set_tooltip_text(_("Seek backward"))
        self.player_toolbar.insert(button, -1)
        # win.seek-forward
        button = Gtk.ToolButton(
            label=_("Seek _Forward"), icon_name="media-seek-forward")
        button.set_action_name("win.seek-forward")
        button.set_tooltip_text(_("Seek forward"))
        self.player_toolbar.insert(button, -1)
        self.player_toolbar.insert(Gtk.SeparatorToolItem(), -1)
        # Volume button
        self.volume_button = Gtk.VolumeButton()
        self.volume_button.props.use_symbolic = False
        adjustment = self.volume_button.get_adjustment()
        adjustment.set_lower(0)
        adjustment.set_upper(1)
        adjustment.set_value(self.player.volume)
        aeidon.util.connect(self, "volume_button", "value-changed")

def _confirm_close_document(self, page, doc):
        """Close `page` after asking to save `doc`."""
        title = _('Save changes to document "{}" before closing?')
        title = title.format(page.get_basename(doc))
        message = _("If you don't save, changes will be permanently lost.")
        dialog = gaupol.WarningDialog(self.window, title, message)
        dialog.add_button(_("Close _Without Saving"), Gtk.ResponseType.NO)
        dialog.add_button(_("_Cancel"), Gtk.ResponseType.CANCEL)
        dialog.add_button(_("_Save"), Gtk.ResponseType.YES)
        dialog.set_default_response(Gtk.ResponseType.YES)
        response = gaupol.util.flash_dialog(dialog)
        gaupol.util.raise_default(not response in (
            Gtk.ResponseType.YES, Gtk.ResponseType.NO))
        if response == Gtk.ResponseType.YES:
            self.save(page, doc)

def _show_io_error_dialog(self, basename, message):
        """Show an error dialog after failing to read file."""
        title = _('Failed to open file "{}"').format(basename)
        dialog = gaupol.ErrorDialog(self.window, title, message)
        dialog.add_button(_("_OK"), Gtk.ResponseType.OK)
        dialog.set_default_response(Gtk.ResponseType.OK)
        gaupol.util.flash_dialog(dialog)

class Framerate23976(aeidon.EnumerationItem):

    label = _("23.976 fps")
    value = 24 / 1.001


class Framerate24000(aeidon.EnumerationItem):

    label = _("24.000 fps")
    value = 24.0


class Framerate25000(aeidon.EnumerationItem):

    label = _("25.000 fps")
    value = 25.0


class Framerate29970(aeidon.EnumerationItem):

    label = _("29.970 fps")
    value = 30 / 1.001


framerates = aeidon.Enumeration()
framerates.FPS_23_976 = Framerate23976()
framerates.FPS_24_000 = Framerate24000()
framerates.FPS_25_000 = Framerate25000()
framerates.FPS_29_970 = Framerate29970()

def _check_file_not_open(self, path):
        """Raise :exc:`gaupol.Default` if file at `path` already open."""
        for page in self.pages:
            files = [page.project.main_file, page.project.tran_file]
            paths = [x.path for x in files if x]
            if not path in paths: continue
            self.set_current_page(page)
            message = _('File "{}" is already open')
            self.flash_message(message.format(os.path.basename(path)))
            raise gaupol.Default

gaupol.conf.connect_notify("application_window", "toolbar_style", self)
        gaupol.util.pack_start(vbox, self.main_toolbar)
        # win.open-main-files
        button = Gtk.MenuToolButton(
            label=_("Open"), icon_name="document-open")
        button.set_menu(Gtk.Menu())
        button.set_is_important(True)
        button.set_action_name("win.open-main-files")
        button.set_tooltip_text(_("Open main files"))
        callback = self._on_open_button_show_menu
        button.connect("show-menu", callback)
        self.main_toolbar.insert(button, -1)
        self.open_button = button
        # win.save-main-document
        button = Gtk.ToolButton(
            label=_("Save"), icon_name="document-save")
        button.set_is_important(True)
        button.set_action_name("win.save-main-document")
        button.set_tooltip_text(_("Save the current main document"))
        self.main_toolbar.insert(button, -1)
        self.main_toolbar.insert(Gtk.SeparatorToolItem(), -1)
        # win.undo-action
        button = Gtk.MenuToolButton(
            label=_("Undo"), icon_name="edit-undo")
        button.set_menu(Gtk.Menu())
        button.set_is_important(True)
        button.set_action_name("win.undo-action")
        button.set_tooltip_text(_("Undo the last action"))
        callback = self._on_undo_button_show_menu
        button.connect("show-menu", callback)
        self.main_toolbar.insert(button, -1)
        self.undo_button = button