Chidgey is correct - the skill lets you translate in both directions (although I believe that the loresheet is optimised for translations from <Named script> to Common - so translating in the other direction may be a bit slower).
Note that if you do create documents in the named script you should clearly indicate on them that they require the appropriate Translate Named Script <x> OS to translate to common - otherwise someone who finds it could decode it, just like any other substitution cypher, without having the appropriate skill.
Be aware, however, that this is likely to be ruled as marking the document as IC, making it stealable as per the rules on IC Theft (rulebook, page 44)
Rich Whitaker
Forum Moderator (yes, that means this post is official unless it explicitly states otherwise)