i really hope the next time we see Luna, she drops the old-style english. it doesn't fit, and when we first saw her she didn't speak in that way either.
no "We are sorry! We missed thou so much(eth?) big sister!", simple "I'm so sorry! I missed you so much big sister!"
it still doesn't make sense that she started to speak like that in Luna Eclipsed, she had fully recovered, which took time, and obviously spent most of that time with Celestia (who uses modern-english)
if they used that language in the past, she would have picked up on most of the modern language within the time between the two seasons.