Didn't have an issue I could not google so far, also it might be a doozy:

I've got a PHP site that mixes Wordpress with Kohana - Wordpress for that blog, and Kohana for that custom functionality. This is accomplished utilizing a Wordpress plugin that stitches them together.

This is effective except both of them define a __() internationalization function, with various arguments etc. so once wordpress has overridden kohana's __(), if kohana calls __() it explodes.

I am not that acquainted with PHP so this can be naive, but should not these items be namespaced? Can there be anyway apart from altering the origin of either framework to permit them to call their very own particular __()?

Using namespaces might be a tiresome task as it might require you plenty of code change. I recommend changing the __() function in Wordpress with a few other title.

I have done some work integrating Wordpress with Kohana. See this post. It's simpler to relabel and replace __() in Kohana than to do this for Wordpress, believe me.

Namespaces are new in PHP 5.3. Just about all existing software projects avoid using them, since they would like to be suitable for older versions of PHP. Many (most?) aren't even object oriented! You can replace every demonstration of __ with another valid (and different!) function title within the projects, but that can make upgrading that project difficult despite the fact that it's most likely the very best solution.