E.g. see this history, where 4-digit page size decrease is formatted as "-2 414" (with a space), while 4-digit page sizes and page size increases are without a space. It is correct that 4-digit numbers should be formatted without a space, while numbers from 10 000 use space as a separator.
Also, correct minus sign in Estonian is minus (−), not hyphen-minus (-).
Edit: If I'm not mistaken then the rule in LanguageEt.php currently doesn't consider negative numbers and what we want is more like the rule in LanguagePl.php.