en_HR is locale meant to be used by computer users whose native language is Croatian, but who are primarily used to US English based interface. Therefore en_HR features US English messages, and US style of writing numbers. US numeric style is chosen because of the decimal separator - in US style the decimal separator is `.', which is commonly used in mathematics and by SI, while Croatian decimal separator is `,'. If you would rather use Croatian numeric style, then use en_HR@hrnum instead of en_HR. Collate, ctype, monetary, paper, telephone, measurement, name and adress settings are the same ones from hr_HR locale. Date and time format conforms to ISO 8601 standard.
Here: en_HR — en_HR@hrnum
Unfortunately, at this moment there is only HOWTO for Gentoo GNU/Linux users, but you may still find it useful. If you use another distribution (or operating system), and found this useful, please fell free to contibute by creating a HOWTO for your ditribution or OS.