Language is changing in a middle of checkout

J2.5.4, Falang, latest hikashop

My site has two languages: Lithuanian and English (default). When user in Lithuanian part of site adds product to cart, he is asked to login or register. When he registers site language changes to English(default) (but only part of it, because main menu is left in Lithuanian). It seams that only hikashop part of site changes language. If i refresh page in this point it goes completely to Lithuanian again because in url there is LT language symbols, but customers don't know that they need to refresh page. How can i force the site/hikashop to stay in the same chosen language and not to jump to default in a middle of checkout process?

www.pharmaDNA.com

but now i've changed default language to LT and everything seems ok. So the question is why hikashop jumps to default language in a middle of checkout process?

yes, because now i've changed default site language to Lithuanian. Tell me when you will be looking, i'll change it back to English, and then you'll see.

but i want to make default language English and i'm planing to add another language soon, so please can you look at my site when you'll back?