No matter how skilled a translator could be, he/she can come across new vocabularies or idioms which are new to him/her. It might be a technical term, a folkloric expression which has no-equal in the target language, a brand name or just a new word!!
What do you do in such cases?!
I work on the English to Arabic pair and this is my methodology to deal with such cases.
I look it up in Golden Al-Wafi & Google translate dictionaries; this works only with non-technical single words that are unfamiliar to me.
But for most cases, I use Google definition to learn about new terms.
(For those who don't know what's Google definitions, just type "Define: X" in Google's search bar and replace X with anything and Google would bring up an ultra-summarized definitions of all the meanings X might refer to!)
And that's just one of the many reasons I love this job, because everyday I learn something amazing!!
What about you?!!