Simplest way : you could copy English.txt to Lithuanian.txt then start editing.
More details, from README.txt :
To create a language pack :
- First run LFS. This will create a file "English.txt" in a folder
"data\language". Please do not edit English.txt as it will be
overwritten each each time you start LFS. Instead, make a copy of
the file with the name of your language replacing "English".
- After creating your new file, it can be edited in a text editor.
- Load your language in Options...Player.
- Reload the language file any time with SHIFT+F5, for convenience.
- The help.txt file can also be edited, in the data\misc folder, copy
the file help.txt to a new file help_XXX.txt (where XXX.txt is the
name of your language file).
- If you plan to make a new translation, we recommend that you contact
us about it - we now have a special online translation system and it's
possible someone else is already working on the language you want to
translate - we may be able to get you in contact with them or set up
your language for you to edit online.
Offline translation program (this may help) :
http://www.lfsforum.net/showthread.php?t=1299
Online translation system (this is the best way) :
Please contact Victor with the "contact us" button at
www.liveforspeed.net