My children aged 11 and 7 use Wikidot (www.wikidot.com) and are quite happy with it. They can add their text and images in one step with no problem via Wikidot's dataforms functionality (like a CMS), adding tags is easy and they create new pages and categories. The only thing they need consistent help with is creating the code to list pages in each category but that's not surprising.

I am an admin of Wikidot as well as a professional developer on the platform so naturally have a vested interest, but my kids find it easy to use and there are  hundreds of other young people who use it because Wikidot is used extensively in an educational setting for assignments, projects, lesson notes etc.

Wikidot has a very active community (community.wikidot.com)where you can get help and advice at any time and get answered very quickly as our admin team members are all round the world.

Yes, the interface (buttons, menus etc) is available in Spanish. And if you see a problem with the translation you can improve it at translate.wikidot.com

You can use your own domain, all of my sites on Wikidot use custom domains, not Wikidot ones. For example the one in my signature below, or sites www.rfpg.org. It's very easy to set up.

But if you want your own hosting plan, i.e to host your own Wiki, then Wikidot is not for you.