Non-English characters are removed from the URL in ISO-8895-1, because there is no way to transliterate them to ASCII. Since you have a foreign language site, don't use that character set; it is being phased out by vBulletin, by VaultWiki, and is mainly for Romance languages. Use UTF-8 instead, it seemed to work fine on your site before, except for a few characters. I'm surprised it worked in ISO-8859-1 at all for you, because that set supports many less characters than UTF-8.
Although UTF-16 and UTF-32 support orders of magnitude more characters than UTF-8 even, as I mentioned before vBulletin doesn't support those sets. The byte order for them is different, and vBulletin isn't programmed to send its output or read input in that way.