Those rules do seem very, err, bureaucratic. As a family we've been going through the process of gaining Irish passports for myself and my children (my wife doesn't qualify) for a few years now and the requirements are so much easier. If you have a parent born anywhere on the island of Ireland - north or south - you're automatically Irish and just need to apply for a passport. If you have a Irish grandparent (as my kids do), send in the paperwork to prove it and you'll get citizenship. Then apply for a passport in the usual way. Beyond grandparent level it doesn't work and neither does it if the parent dies before you apply. It takes a while as all these things do (20 months for my son, daughter's application still in the system) but no tests or employment records etc.

My son has worked in Sweden for four years on his UK passport and ticks all the boxes for Swedish citizenship by naturalisation. The application does take about three years to go through but unlike Germany there's no language test or Swedish history/ lifestyle exam to pass.

Faced with Brexit uncertainty he applied about this time last year and kept his fingers crossed as his current work contract runs out about now. Three months in though the Swedish govenment had a change of mind/ heart and fast tracked the qualifying Brits in a few weeks. Citizenship came through in three weeks and his passport in two more. So at the moment he has UK, Irish and Swedish passports and no one only requirement/ restriction. If he had to choose only one I'm pretty certain he'd stick with the UK for work reasons.