In order to publish in multiple languages you simply have to create a publication for each languages as if it were a different publication.
When you upload the publication in Büttonpublish, add each language inside of the issue/publication and upload its content for each language.
In the case of uploading in different languages, the licenses conisder a publication in different languages for the price of one. In other words if you have a publication in 3 languages, you will only pay for one.