I was messing around with the different languages, and was in Shakespearian English, when I ran /fill. I do one coordinate point at a time, so get an error message before putting in the second point and block to fill with. I was reading it later, and I saw that what was misspelled.
This is a very simple bug to reproduce, as you just have to do "/fill ~ ~ ~" and then hit enter while your language is Shakespearian English, and look at the message that comes up.
I have not tested this on the snapshots, but I will later today.
Thank you for your report!
However, this issue is Invalid.
Translations for languages other than "English (US)" are done by the community and take place on the Crowdin Minecraft Translation Project.
Please use Crowdin for suggesting and adding translations.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki