This actually happens all the time -- some new word is invented, often in English, and now the other languages have to find a way to deal with it.
One possibility is to take the English word, and do the minimum necessary modification to make it feel natural, such as add or modify a suffix... more or less what a neural network trained on similar kinds of words would do. Another possibility, if the new word is composed from existing roots, use the translations of those roots and try to connect them in similar way.
Sometimes the rules do not allow an analogical operation, for example, in some hypothetical language it could be very unusual to derive the adjective "existential" from the noun "existence", so you might end up with a more clumsy phrase for "existential risk" such as "dangers threatening the existence" or similar. Maybe not this specific example, but sometimes other languages are less flexible in some places than English.
Ultimately, the rules are not 100% exact; even if you translate the term breaking some of the rules, as soon as the translation gains momentum, people will use it, even if some language purists would complain.
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