If not, is this a licensing issue?
Speaking as the former editor of Worlds of Cthulhu, yes it was, back in the day. Only Chaosium could publish foreign licensee Pegasus Spiel's original German language material in English. That was back in the 2000s. What the situation is under new Chaosium I know nothing of.
There is also a financial disincentive to publish foreign language material in English if the original game is in English - the material has to be translated and edited, the original author or publisher and the translator have to be paid making foreign material more expensive than original English language material. Plus there is a pool of material already in English that the foreign material has to compete against.