Wikibase has UI translations to Spanish. You can see them on Wikidata for example.

Hi! I'm the one who brought this up at the Hackathon (just before the showcase session, so I may not have explained it clearly, sorry about that!).

What I was referring to are a few translation gaps specifically related to Wikibase Cloud:

• While the main UI is translated into Spanish, there are still a few parts that remain in English even when Spanish is selected as the interface language (mainly on the left side of the site).
• When you create a new Wikibase instance, the main page includes some guidance and recommendations, but these are shown in English, regardless of the UI language setting.
• Additionally, the wikibase.cloud landing page itself is only available in English. Since I’ve been working on promoting Wikibase Cloud in Latin America, this has been a barrier for some new users who want to create their own instance.

I’ve started working on Spanish documentation to address this, and I’m happy to contribute more (e.g. translating any docs that are not yet available in Spanish). However, I’d need some support from the Wikibase team to make these translations available in the UI and possibly explore translating the main webpage as well.

I think that's all :-)

I dont believe any part of the wikibase.cloud UI is currently translated into any other languages than English.
The code repo is https://github.com/wbstack/ui/tree/main
That would need to have some form of string translation system added.
likely translatewiki etc would make sense

I'm not familiar with VUE applications but, after a small Internet checking, seems the approximation to i18n'd (internationalize) the code is using Vue I18n.

Side bar translation ticket: T380370
Translatewiki ticket: T337026