a mistyped update file in Mojang downloads related to the en_us.json, they renamed it wrongly to en_ud.json
Comments 2
It's a bug in Forge: https://github.com/MinecraftForge/MinecraftForge/pull/5105
MC-136129
launcher language json
Resolved
Invalid
0
Thank you for your report!
However, this issue has been closed as Invalid.
en_ud is for upside down English, there was no typo