Not a lawyer but I suspect it would depend on the country.

As an example there are clauses written into ToS which don't allow refunds on digital purchases. These work fine in the US but are illegal in countries with stronger consumer protections like Australia. US companies do still have to obey local laws - at least when it comes to the sale of faulty goods.

It’s complicated...

I would suspect (not a lawyer) that the main issue will be jurisdiction.

As a consumer in the EU, jurisdiction in matters with commercial entities is the consumer’s place of residence. But HN/YC isn’t in the EU, and I don’t think there are any legal agreements b/w the EU and USA that are relevant here. Free trade agreements tend to include such issues, but TTIP’s well-known fate means this is left to the parties to specify in any contract.

Then, there’s a difference b/w HN and YC. HN’s relationship to users is that of a commercial entity to consumers. But YC investing in your startup isn’t. Consumer protections would not apply even if YC were in the EU.

To summarize: yes, the arbitration clause, at least of YC, would apply to the same extend as if you were a US citizen.

Also not a lawyer. To be covered by Germany's consumer protection law, you need show that you are end consumer of a commercial product or service. I don't see how that would apply to YC/HN.

If you could pull that part off, I think you could take YC to court in Germany, and even achieve a favorable judgement. However, I don't see any way how you could enforce the outcome, except if YC has assets in Germany.

I am not a lawyer, but I highly doubt it, if all you've done is create an account. There is no mention of the arbitration clause in the account signup, so you literally can't agree to it during the signup.