Due to its location near the equator, weather in Trivandrum does not vary much seasonally. You should plan for highs of 32C/90F and lows of 25C/75F. December is not the rainy season in Kerala, however some unexpected showers would not be out of the ordinary.
Kerala food has many options for vegetarians and non-vegetarians alike! Much of the cuisine is rice-based, although Malabar Parottas are world-renowned for a reason. Aside from various vegetable curries, dosas, idlis and appams, Kerala is known for its seafood and beef offerings. For more information, please visit: https://www.keralatourism.org/kerala-food/ North Indian food is also easily available throughout the state as are many Western fast-food chains. All hotels are likely to serve North Indian and Western cuisines as well.
Generally, no. English is commonly spoken within Kerala, especially by those working in the hospitality industry.