It’s not possible to do this on a category basis without using a plugin.
You could try enabling the ’ support mixed text direction’ setting. This will set the dir attribute for text on your site based on the direction of the text. This will also let you have mixed text direction within a post. as long as the text is separated by an empty line.
Text that is entered in the composer will default to the direction based of the user’s locale. If their locale is set to an RTL language, text entered in the composer will have a right-to-left direction. This direction can be overridden by clicking the Toggle Direction button that the setting adds to the composer. (This was developed for an Arabic coding site.) Text in the preview window should always appear in the correct direction.