(I am guessing this is not a core issue + it is a single issue and not two separate ones.)
I get these upon opening a node creation page where the content type's Multilingual support is set to 'Enabled, with content translation':
* Warning: strlen() expects parameter 1 to be string, array given in drupal_validate_utf8() (line 1503 of /var/www/d7test/includes/bootstrap.inc).
* Notice: Array to string conversion in filter_xss() (line 1335 of /var/www/d7test/includes/common.inc).
I don't know if this helps at all, but in other warnings I used to receive in the past (concerning completely different issues), instead of the server path of the file I used to get a URL with the site's address.
The help text under the node's Title text field is simply 'Array' (see attached screenshot).