So you convert crypto to fiat while living in Germany. And then you don't really have to move to a country with asset declaration for wealth tax - most countries don't have this.
But if you still do, source of fund for your assets is usually not requested.
More of an issue is that banks sometimes require SOF, and here a tax declaration is one of multiple ways to show SOF. But I wonder if it doesn't show up in the German tax return even with 0% tax. The tax rate isn't the issue, just that you have paperwork for it.
Here is what I︀ would have done though. Skip Germany, just get out of the Romanian tax net, and︁ live in some fun country in Latam or Africa or Asia that doesn't care about︂ personal capital gains. Then convert all the altcoins to Bitcoin and keep the Bitcoin, it's︃ better money than fiat anyway.
But if you need some fiat for spending, convert in︄ small batches via crypto friendly EMIs like Xapo, Zen, Verifo, Yoursafe etc, and/or via exchanges︅ that also offer bank cards/IBAN's like Swissquote, Nexo, Swissborg and others, and/or p2p within the︆ Bitcoin community.