"Never any US to UK translation."
Why is it that Americans seem unable to deal with UK English. We in the UK seem to manage to deal with the US version. We have to. There is never any US to UK translation.
The mapping from en_UK to en_US is (very) many to one with the consequent loss of meaning for the great many concepts the American intellect is unable to grasp.
Mapping from en_US is basically choosing the en_UK word or concept from the shallowest available which even densest of the pommy polloi can manage in their heads.