Correct. But ugly. Instead of characters you should try HTML entities ä = ä Ä - Ä ...etc... ß = &szling; http://symbolcodes.tlt.psu.edu/web/codehtml.html

Amazon.de can display products with umlauts. Ask their support how to encode/input umlauts properly so they do appear in the product name. One possible reason might be that your browser is using a chinese encoding, so amazon rejects these, and therefore you may have to change some browser settings. But that is just a guess. HTML-style encoding might or might not work, ask them. It will look a lot more professional with umlauts instead of the substitutions, though in principle the substitutions are equivalent.