It’s not hard and doesn’t need language awareness; I described how to detect it: if there’s no space before an end-of-line em dash, suppress the segment-break-replacing space.
replyThere seem to be some locales or styles that use asymmetric spacing. From the Zen of Python—note different spacing based on context and position within the sentence:
reply There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
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Namespaces are one honking great idea -- let's do more of those!