I got this error from Codestyling Localization in reference to several plugins:
Loading Issue: Author is using load_textdomain instead of load_plugin_textdomain function. This may break behavior of WordPress, because some filters and actions won't be executed anymore. Please contact the Author about that.
But when I contacted the authors I got this reply from the author of Contact Form 7:
This error message is not generated from Contact Form 7 plugin or WordPress itself. I guess one of other plugins (maybe a translation plugin?) you're using is generating it.
The functions load_textdomain() and load_plugin_textdomain() are not equivalent. You can specify .mo file path with load_textdomain(), while you can not with load_plugin_textdomain(). Contact Form 7 has a function that allows you to create a form template set in any language. It's necessary to use load_textdomain() to realize that.