They say here that ICU is used on many platforms. But I can't find what version comes with OS X and Windows. In Linux I suppose a package-manager would tell me.
UPDATE: Changed CLDR to ICU
I don't know whether platforms come bundled with ICU. For sure, Windows does not. Unix-based platforms might. For one, apparently OS X comes bundled with some version of it.
If the platform delivers a full bundle of ICU you can test the version of ICU using the command:
$ uconv -V
Which will print the version. The latest version is 54.1, it looks like this:
uconv v2.1 ICU 54.1
In addition, if your platform has Qt installed, it is possible it has been compiled with ICU support, but this is not a necessity.
If you want to use ICU, you're probably better off shipping it with your product as opposed to rely on what is on someone's system. ICU has a fairly regular update cycle, chances are that pre-installed ICU libraries are out of date.