Lead rudely demands fixing alleged error on weekend

Obviously the risk of being sacked according to your response cannot necessarily be averted, and is something only you can judge.

Unless you have profoundly important plans for this particular weekend, then these things are often about some kind of principle of the matter, such as the need for rest, respect for plans, or the need to set boundaries on a manager whose only limit is what they can get away with.

It's hard to tell exactly what principle is at stake in your case here. You acknowledge such weekend availability is not a normal practice in your department (nor culturally), and you've been there 18 months (so enough time to indicate this demand for weekend work is very exceptional).

I think what's really happening here is that your lead is annoyed that a bug he considers your responsibility was not fixed, and both as an act of contrition and since it is now an emergency, expects you to fix it immediately.

If so, then I think your best course of action would be to join in the work and solve the problem, whilst either stating your annoyance (if the issues involved are mild and/or your fault is ambiguous), or (if it really raises a systematic issue) stating your desire to have a more thorough conversation about it later next week.

I think as well, the fact your lead mentioned the potential need for availability on Friday suggests there was some advance thought. If such availability is strictly necessary during future deployments, then you might want to open a conversation about the need for more notice and specific agreement, and compensation (at the very least, time off in lieu).

I think it's true that in general, European workplaces have stricter boundaries around the invasion of personal time from work life.

If this hasn't come up in the first 18 months of the job, it's entirely reasonable to politely ask how necessary this weekend work is, and what expectations are going forward. It's also reasonable to push back against those new demands, though I would advise joint problem-solving as a first resort. Eg, "with this mechanism, we can release without taking the shared database offline, so it can be done at the end of a normal work day". Is the release process slow and infrequent? Might you not just have observed it before?

It is also not uncommon to be on call to support releases, across the world in my experience. If you don't like being called in your personal time, go to extra effort to ensure your code is of high quality and deploys cleanly in other environments without error-prone steps.

Though it is not your main question, as described here, the issue investigation could have been better and more professional. If you are specifically asked about a potential issue related to a coming release, you should respond quickly - I would suggest within a few hours. If you think the issue is so much less important than your other work that it should wait "a while" (weeks?), why are you assuming that? Code is only worth anything when it runs in production, so this issue is more important, because it relates to code about to be in production. If the issue is a misunderstanding, not a bug, coming back with a clear technical explanation of why it's not a bug is the most useful thing you could be doing. If you think something else should be a priority, you should explicitly check with the team lead that your understanding of the priorities is correct. Passing QA is good but not a magic wand, and understanding what the team priorities are, and communicating clearly about issues and priorities, are vital skills for a software developer.

The lead may also have been assuming that when asked to look into an issue you would go and take care of it, not that you'd have to be chased again. Best check with them what the potential impact is and whether the production release needs to be stopped because it hasn't been resolved yet.