I know this site has been a pain when you have some special characters (n-tilde, umlauts, etc) in the name of products you are using. There is a solution.
The standard comment interface is WYSIWYG (what you see is what you get), but it doesn't accept those characters. But one of the little buttons at the top of the comment box allows you to type your comment in html, and therein lies the secret. Before you start writing, click the little button on the end that looks like a page with <> on it. That gets you into html mode. then write what you need to write, but when you get to the special characters, use html code for that character:https://www.utexas.edu/learn/html/spchar.html
so instead of "Goteborg's Rape" you type "Göteborg's Rapé" to get the correct accent marks. Post it from the html mode, and your special characters will appear.