I've always stored English, French and Japanese text strings in a same column without paying much attention to mysql charsets and collations. Since I've never noticed any problem, I'm wondering: what are they for? ( I've read the documentation but it's obviously targeted to experienced admins ... so I'm still clueless )

This week, I've installed the new version of mysql on my windows box (AppServ install) and I accidentally set default-character-set to UTF-8. Now, when I use SQLyog, all my fields have the collation field set to UTF-8 ( all my web pages are encoded in ISO or JIS).

Will this change have any bad repercussion?

What should I do to have my database safely store any language from a non-UTF-8 website?

Can I leave the collation fields empty?

Is it bad to have multiple languages stored in a same column?

Many many thanks to the ones who will share some hints :)