Machine Translation Evaluation

Hi all, I'm currently working on the project aiming to create a Live Translation tool helping people speak to each other in a different languages in real time.

Regarding the machine translations, I was wondering what are the current best practices regarding the machine translation evaluation? I know there is a manual approach using professional human translators and also a range of automatic approaches, such as BLEU and METEOR or its combinations... but it is all just my theoretical knowledge without any real experience.

I would be grateful if you could help me understand this topic better, refer me to some resources or just briefly educate me what are the current main trends, topic to follow and best practices in the machine translation evaluation?

Thanks a lot!