Hi Patrick,
You are certainly welcome to help – and yes, we’d be delighted to offer a coupon if you contribute a substantial number of translations 🙂
For the most part, the process is managed over here:
translations.theeventscalendar.com
If you find the line-by-line editing is too limiting and prefer to work on this locally using a tool like PoEdit, please feel free and simply share the resulting work by uploading the .po file via your own WP site/a service like Dropbox (and link to it here in the translations forum).
Thanks!