Standard used for coordinates in Lithuania is called LKS-94. There are many reasons for that, which are beyond importance for the common case of projecting things on a map, like googles or others. That requires WGS-84 standard coordinates.
Easy way for transforming these ad-hoc is here: https://www.geocad.lt/nav/
Also we're adding up some code to help out developers. Pull requests for other methods or other languages are welcome and appreciated!