The developers or official support can provide the best answer but from a technical standpoint, yes you can add additional payment gateways. Even in the free version, you'll see a gateway folder in the plugin's zip file where you can see how the various gateways are done. A skilled developer can add gateways using those as base examples.
As for translations, it's totally possible to translate the plugin, as it's developed according to best practices for WordPress. Whether or not someone's already provided a translation would be something for official support to answer. You could always contact them via their contact form for more info. They're quite fast and very helpful! :)