Just had a look at the paper. They indeed assume that long dependencies are hard and that languages therefore tend to optimize for short dependencies. They al

Just had a look at the paper. They indeed assume that long dependencies are hard and that languages therefore tend to optimize for short dependencies. They also argue that some languages (like German) may have longer dependencies because other aspects of their grammar make it easier to process those dependencies than would be the case in short-dependency languages like English. This suggests that languages that are more optimized for dependency length may be less optimized with respect to some other aspect of processing. Languages may thus make different tradeoffs with respect to the various sources of processing difficulty. This means that German may have seemed hard to Mark Twain not because it is intrinsically harder but simply because it makes different tradeoffs than English.