Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Assume that the site is still in it's design phases so there's no initial work to pick one over the other from the start.
With UTF-8 you have increased flexibility over ISO 8859-1. The former can encode any character included in Unicode while the latter is limited to Western European languages.
ISO 8859-1 ("Latin1") doesn't include, for example, Greek, Hebrew, Arabic, Cyrillic, Chinese, Japanese and Korean, etc.
Required, but never shown