Hi there,

If you want to translate the theme strings such as All, Previous, Next then the theme is already translated to Spanish along with 17 other languages:

https://documentation.laborator.co/kb/kalium/translation-introduction/#pre-translated-languages

But if you want to have a multi-lingual site then you will have to use a plugin for that and we recommend using WPML:

https://documentation.laborator.co/kb/kalium/translating-kalium-with-wpml-plugin/