As a person who manages a team of technical people, but not a lawyer, I can tell you that my assessment of this request when it happens is 'how important is this person to the team'?

I've got team members who have 8-12 weeks of leave and an adequate replacement for them would take months to recruit and then months to get up to speed, and they know that if they want leave the best thing is to give me 3-4 months notice, so I can either get someone trained up or work out contingencies. The less notice you give me of your multi-week absences the more work I have to do, and the unhappier I will be. The other thing is when I find a person for your 3 month absence, after a 2 month job search, and I train them up over 2 months to do your job, are you confident that when you return you're going to be as important to the team as when you left? It's why senior staff take short 1-2 week holidays, and not 8-12 week absences. People who are serious about their jobs and careers don't go traipsing over Europe for 8-12 weeks.

On the other hand, I have team members who I can advertise a role for tomorrow, and because the job market is so rubbish at the moment, I can have someone interviewed and ready to go in 2-4 weeks. And because those team members have fairly generalist skill sets, they only take 1 or 2 weeks to train. I'm not too bothered if people like that want to take 8-10 weeks leave, as we'd probably just get someone on contract for the duration of their absence, or spread the load of that persons job over the team.

From your description, I'd say you fit into the second category, but if you show the responsibility and consideration of someone in the first category by giving plenty of notice (>3 months), by telling your employer you really want a job to come back to, that might be the way to go, assuming you want to continue working there, and you indicate that you're not really sure of that.

Alternately, you could do something like this --> https://www.youtube.com/watch?v=KonQoIqOPBI