Language switch on product page returns 404

Question

Having trouble switching between languages on product view of Magento 1.8.1.0. Already tried extensions/solutions from Vinai and DGagliardi resulting in same one-way redirection behaviour.

Our case:

VIEWS:

• Lithuanian (default)
• English

Product info:

• URL default: product-title-in-lithuanian
• URL lithuanian: "Use Default Value"
• URL english: product-title-in-english

Behaviour

• from Lithuanian view:
  • being on /lt/product-title-in-lithuanian
  • switching to english sends to /en/product-title-in-lithuanian
  • which itself redirects properly with 301 to /en/product-title-in-english
• from English view:
  • being on /en/product-title-in-english
  • switching to lithuanian sends to /lt/product-title-in-english
  • which DOES NOT redirect to /lt/product-title-in-lithuanian and ends with 404 error

Any tip what could be the problem here?