wrong hreflang issue

Hello,
I am an old fan of your plugin and it’s working as a charm.
However recently I encountered big SEO problem. Google seems not to recognise correctly the language and there are italian version pages (snippets) in the bulgarian search results. Basicly, it’s a mess. (and this. having geotargeted and registering the various sites in webmaster tools)

Maybe a clue …On a /en/ page I see rel=”alternate” hreflang=”bg” which is the original language of the website. How can I change the language indicator correctly (I’m not a code poet so I’d search for something dummy)
So how can I, if so, change this marker so that Google recognises the language correctly?

Thanks a lot for your support!

https://wordpress.org/plugins/transposh-translation-filter-for-wordpress/