The translation keys used for /worldborder set when the size is too small (less than 1) or too big (more than 60000000) have a period at the end: commands.worldborder.set.failed.small. and commands.worldborder.set.failed.big. (for the internal translation keys). This does not match the pattern used by any other keys (keys with a dot at the end are in some places other, but they always have additional text concatenated afterwards), although it has no in-game effect.