Constructing a collator from rules is quite an expensive operation. In ICU 2.6,
code was introduced that will construct a collator for a locale from rules if
the image is not present or is stale.
It might be beneficial to have a cache for images of collators constructed from
rules, so that repeat constructions are faster.
On the other side, keeping any cache around involves a certain amount of book
It should be investigated if this stunt would be worth the effects, given the
usage model for collation.