While the basic syntax is relatively easy, knowledge of APIs (whether standard or third-party libraries), design patterns and conventions takes time (and practice) to master regardless of skill level.
Being an expert at a single general-purpose language will often make you more productive as you can focus on the business problem at hand rather than spreading yourself thin across different languages where you'll perform worse until you become an expert at them (which is unlikely for anything more than a handful of languages and even that requires working with them regularly).
Being an expert at a single general-purpose language will often make you more productive as you can focus on the business problem at hand rather than spreading yourself thin across different languages where you'll perform worse until you become an expert at them (which is unlikely for anything more than a handful of languages and even that requires working with them regularly).