At least in the EU, AldiTalk offers 4G LTE with plans of up to 5.5 GB for 12.99€ / month[1]. I am not sure, though, what is the price per MB when a stork leaves the EU.
Most, if not all, EU carriers (I assume including this one, but don’t speak German) have a limit of how long you can actually be outside your home country. After that period they either terminate your contract or withdraw the free EU roaming (which is perfectly legal per the regulations).
"Complying countries: in major EU countries like the UK, Netherlands, Belgium, Germany, Spain, Portugal, Croatia, Cyprus, Malta and Greece there is a general adoption of the principle without any limitations or FUPs on almost all prepaid plans offered."[1]