Just to be clear (wrt. some comments/answers here) about brazil: yes, it's true, you can't be forced to sell your vacation days. But you also can't force your employer to give you 30 consecutive days of vacation. The law on Brazil is that an employee gets 30 days of vacation yearly, but (disclaimer: because of legislation changes in 2017, the second item was different, here is the info for early 2023):
- the employer sets the date (it's generally courteous to agree upon, or at least the employer gives an window of days ─ for instance, once I was told I couldn't take vacation 3 months before Carnival because that was our peak season);
- the vacation can be divided in up to three periods, but one period must be at least 15 days long, and every period must be at least 5 days long (see footnote for details about 2016);
- during vacation, you get a bonus of a third of the salary (counted by days) you'd receive in the period you're off (if you're off for 10 days, it's a third of what you'd receive for those 10 days only);
- the employee can ─ but cannot be forced to ─ sell up to 10 days, getting the full salary he'd receive for those days plus a third as a bonus (so, for example, my monthly salary is 1000, I sell 10 days, I'll receive my full salary, plus a bonus of 333 [equiv. to 10 days] + 111 [a third of those 10 days]).
Bottom line is: the employer has the final word on you taking 30 days consecutively
Nevertheless, if you have children and want to take a big vacation during school break with them, or if you want to make a big trip to another continent, you could always try and talk to your boss. Be ready to make concessions like trying to finish or at least progress fast in your project(s) before your vacation, or even asking if he'd give you 30 days if it was on another period, maybe there's another time where it's slower and it's easier to be absent for 30 days.
Before, the second item was as follow (what changed in italic):
- the vacation can be divided in up to two periods, and each period must have at least 10 days (which indirectly means that at least one period would end with 15 or more days anyway).
But the rest of the answer would've been applicable.