UI Translation is on the roadmap: https://anilist.co/forum/thread/3878

The previous version of the site did have a rough Japanese translation as a test - and the new design that came in last summer will make it much easier to do a full translation when the time comes. Will open up translation to users and ideally have as many languages supported as possible.

Stored translation of entry data itself (series descriptions, titles etc.) I'm unsure if will happen - likely not.