"Not possible" is a vast overstatement. We've negotiated imperial territory disputes and hired mercenaries on contract with pantomine. You get there eventuall

"Not possible" is a vast overstatement. We've negotiated imperial territory disputes and hired mercenaries on contract with pantomine. You get there eventually if you're motivated & creative. It's about how efficient using the language for that purpose is. If it lacks a lot of specialized jargon, that jargon needs to be unpacked into symbology that does exist in the language both people are trying to use. With any language learning, you revert to more basic forms in a sort of puzzle of "How do I say that?" if you don't have a deep exposure to the vocabulary. An elementary learner might use twenty words of clarification to be certain of communicating meaning where an expert uses six. With ASL, reverting to fingerspelling to bridge gaps in either person's vocabulary or in the existing corpus of well-known ASL vocabulary is also common. But fingerspelling and using long strings of basic words is painfully slow compared to higher bandwidth formats. If two people speak two languages, they can just pick the one that has the best mutual SNR, which allows for the most concise effective communication. Sometimes, that's going to be written text typed into a phone instead of ASL, and sometimes it's going to be the other way around.