Overview:
The Admin would like to have the Validation Rule Messages translated. However, Rule Message Translation records are not created for all languages which are loaded into the Org after the Validation Data Refresh.
Root Cause:
There should be at least one User with the given language for Rule Message Translation records to be generated for that language's Validation Error Messages.
Solution:
Make sure to have at least one User with the language you need the translation for.
Related Documentation:
CRM Help Documentation: n/a