I was reading on zmj's blog about Schadenfreude and schlimazel being "naturalized word-citizens" and it made me wonder - how do you know if you're just using a foreign word, like C'est la vie, or if it has become a "naturalized word-citizen"? For example, according to this site, all of these German words are loanwords.

If it's use of the word, I wonder how that decision is made (for dictionaries and the like). Thoughts?