Language.UNSUPPORTED_FORMAT_PATTERN is intended to catch stray %d and %f placeholders in the translation resources and convert them to %s, since the translation component only supports this.

However, the regex is currently too broad – in particular it will also catch and convert %%dark and %%food (to %%sark and %%sood respectively), despite these being escaped.

This does not directly affect players, but it's a landmine waiting for mod developers and also your own dev team.