That decision depends on what you are doing. If you have an existing website, keep the current structure and adapt the system. If you start new, think about it. If the content is basically identical except for the language, then subdirectories make sense. If it’s completely separate instances content wise (one site just a single page site, the other with subfolders, etc), a multihost solution makes sense. If you have local domain names or brands (my-website.com, meine-webseite.de) then multihost them. But I personally prefer subfolders. From an SEO point of view you have one single domain you have to optimize for.
The whole topic of redirects comes into play if you have old URLs and want to map them to new structure. Makes always sense so that you keep ranking for the pages. On Netlify specifically (dive into the headers docs there) they have features where you can redirect per language or location/country. But in the end, a redirect is not a structural issue, it just moves the visitor where he expects to go.
That probably won’t help too much If you start from scratch then use subfolders. But that’s an opinion only.