I recall having to deal with operating a aircraft with inop seat belt signs and I was surprised that our MEL allowed us to despatch with the signs inop on that particular occasion.
If you have pax who speak a variety of languages and may not understand the crew then getting ground staff (of whoever) to explain the situation before you go in any local languages, will be a big benefit. Thankfully we just had a 50 min sector so I told all the pax that they were not allowed to leave their seats since that avoided any confusion helped to put to stop to people getting out of their seats and possibly injuring themselves when they should really be sitting down!!!