Multi Site Language switcher

I have a multi-site network site. The main site url is example.com (default Korean) and want to have the second language site (example.com/en/ for English) If a user visits the one of Korean page, let's say (example.com/aboutus/) if he clicks the language switcher on the top bar (such as flag buttons to direct English page) I want to redirect him to (example.com/en/aboutus/ - vice verse ). Simple as this.

Is there any similar switcher plug-in for this? or do I have to create some kind of little script? Please let me have your insight.

Thanks.

PS. Language translate plug-in such as translatepress, WPML and etc are not the option to consider since I want to keep the multi-site setting.