Currently, score does properly render each word of an RTL piece of text but the phrase itself is rendered LTR (that is the order of words in a phrase reversed). There needs to be a way to specify that a phrase is in RTL. The current alternative is to type the words in reverse order which is lousy.
Reported upstream: https://sourceforge.net/p/testlilyissues/issues/5325/ . It is a bit odd to have RTL text in a LTR musical partition.
I found another task (dating from 2009) about supporting RTL partitions. The new task links to it.