The edit summary here is not substituted: https://www.wikidata.org/w/index.php?title=Q19908762&action=history
It looks like the issue might be the missing closing */ at the end?
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Yes, the */ is probably missing because the string got cut off, because it is too long. IIRC, the cutoff is even based on bytes, not characters, which makes it particularly problematic for non-ascii characters, which need more than one byte.
We could try to truncate the parameters inside the /*...*/ block, to avoid the */ being cut of. That way, substitution would work - but the message would be constructed using truncated parameters, possibly causing broken links.
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It would also be nice to not have such a hard limit on the length of edit summaries or at least increase the limit (T6714).
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T215422: Migrate Wikibase to use comment_data field instead of SummaryFormatter could maybe improve the situation? If the parameters will be stored in a more structured way, at least not the */ will be missing.