From discussion in #1341:
Lucene.Net.Analysis.Common is missing the Collation functionality. It probably isn't much work. .NET's collator is called CompareInfo. The Lucene docs say that the ICU4J collator is faster than the JDK, but I suspect that in the BCL implementation will be faster than the one in ICU4N in most cases.
These types are currently excluded from compilation via the FEATURE_COLLATION flag not being defined. We should finish the implementation (including the tests) for feature parity with Lucene 4.8.1.
From discussion in #1341:
These types are currently excluded from compilation via the
FEATURE_COLLATIONflag not being defined. We should finish the implementation (including the tests) for feature parity with Lucene 4.8.1.