This is actually a pretty awesome resource! It was pretty interesting to see "-ish" on there. It never occurred to me that there's likely not an exact equivalent to "-ish" in other languages.
I saw this shared on reddit a few days ago, it's a cool idea but the actual words... there exist very few that are actually untranslateable. If you know more than one or two languages, you probably spot some of them pretty fast. (It's funny you mention specifically -ish, that's one of the words I was skeptical about and clicked through to the thread on, and thus knew that people in the thread mentioned various translations.)
The about page mentions that this is a UI for the subreddit of the same name, which is focused on "Post quirky and niche words/phrases from foreign languages that can't easily be translated."
Personally the discussion for possible translations is far more interesting than the slightly misleading subreddit and site name.
blue -> bluish => sininen -> sinisehkö
formal -> formalish => muodollinen -> muodollisehko
apparent -> apparent-ish => ilmeinen -> ilmeisehkö
compressable -> compressablish => pakkautuva -> pakkautuvahko