What is harder? Speech synthesis or speech recognition?

Without question, it is an order of magnitude more difficult to implement speech recognition.

You can do passable speech synthesis knowing nothing about context, grammar, etc. You will get some issues with homographs but other than that you will get recognizable speech. Now, it will be greatly lacking in prosody and stress, so you need to do some language analysis to be successful but it's all doable and been done. There are toolkits out there that will help you build speech synthesis for any language even without sampling.

But the speech signal is just too noise for speech recognition to be done with any level of success without some understanding of language. This is mostly done stochastically these days, so the recognizer will guess what is likely to come next. So unlike with synthesis you need huge amounts of speech data to process. Again there are open source toolkits that will help you get started, but the amount of work you have to do for a new language is huge and the results will never be as impressive as with speech synthesis given the same amount of work.