Well I seem to have fixed my problem although I had to modify the core code which I don't really like to do. Maybe someone can tell me how to extend the languages.php file using a plugin structure. Anyways here is what I changed the code in languages.php to...

global $CONFIG;

$language = $vars['language'];

$value = (string)$CONFIG->translations[$language];

if(!mb_check_encoding($value, 'UTF-8')) {
    $value = utf8_encode($value);
}

echo json_encode($value);

i'm also seeing this in my logs.. i haven't applied this patch yet.. does anyone know any more about this? is this fix in trac somewhere?

Trac is down, but it sounds like one/more of the language files is not valid UTF-8. You probably want to sniff all languages/*.php files for valid UTF-8, but I don't have code on hand to do that. StackOverflow might.

Rob's solution worries me because some strings are probably valid, and running valid UTF-8 through a function that expects ISO-8859-1 could definitely break data.

@Rob, the (string)$CONFIG->... just produces "Array", so this is just sending "Array" to Elgg's JS translation system. Probably not what you intended :)

thanks,

i disabled all the plugins and the messages remain..
i haven't altered the core language file.. soo..
either there is an issue with the core language file (i haven't found a functioning tool to check the file yet), or there is an issue with my server/dbase configuration. 

hmm.. i just notice the databse collation was set to latin1_swedish_ci for a reason i do not know..
is there a recommended collation setting for elgg? 

i've set it back to utf general and converted the tables too.. 
seems to have resolved the issue. 

i was mistaken..
the cause is spam login filter plugin 1.8.2

What about spam login filter is causing the problem? language file?

i don't know presently, the errors are no longer logged when i disabled it and reappear when i re-enable it

There was indeed a character in the language file in that plugin.  I submitted a pull request to the author on github to correct the issue.

Thanks Steve and ura soul for the pointers in the right direction.  the json errors were annoying.