So, I found this post from Tumblr, and I wanted to see if I can help answer it.
I think that Furbys with that shiny label that says "Furby Summit" (ファービーサミット) show that a Furby speaks another language aside from Japanese. There are Japanese Furbys with this label, but they wear Chinese dresses. I don't know much about them myself, but here are a few pictures from listings anyways (one photo is from a blog). Also, I CANNOT confirm if the lamb furby and the leopard furby have custom clothes or if they actually came with the Furbs. Also yes, I am very sure that they were only exclusive to Japan as the post suggests. I cannot remember, but I THINK one of those old Japanese Furby magazines have a bit of information regarding Summit Furbys.
Frog Furby listing (Furby not available/sold): https://www.amazon.it/Furby-GiG-Art-70-800/dp/B00BRVHVJ4
Leopard Furby listing (sold): https://item.mercari.com/jp/m84452854563/
Dalmatian Furby (sold): https://item.mercari.com/jp/m74005558226/
Lamb Furby (sold): https://item.mercari.com/jp/m67497968236/
Snow Leopard Furby (blog post): https://air.ap.teacup.com/hortensie/572.html