Issue with Toolset plugin

The diagnostic of Toolset support team is correct.
Yes Polylang provides some documented api functions of WPML.

This helps themes and plugins developpers (and thus their users/customers) to add multilingual support without writing something specific for Polylang. They can support both plugins in the same time 🙂

But Polylang is *not* WPML and Polylang does not implement internal functions of WPML (otherwise Polylang would just be a copy of WPML which is of course not the case).

However I cannot prevent that some themes/plugins use these WPML internal functions, thus automatically breaking the compatibility with Polylang.

Regarding Toolset, obviously I can’t support a Premium plugin which is not freely available, so I may solve this error because you give enough information for me to solve it. But other errors may appear.
I also don’t expect that Toolset authors will support Polylang, since they already commercialize WPML 😉

Try adding this code in a personal plugin:

class PLL_Sitepress {
	function get_current_language() {
		return pll_current_language();
	}
}
$sitepress = new PLL_Sitepress;

With no warranty…