My daughter told me that they use native speakers for spoken English and Putonghua. Their standard is good and I believe this is a fair comments as my daughter had been studying in an international school in Shanghai. I am fine with this arrangement as you cannot compare PLK with an international school.
I find the books they use are also ok as they can inspire the mastering of good languages.
We did not particularly prepare for LMC. However, at least your child has to speak a complete sentence and show response to teachers' questions. Don't be shy is the key.