I have now enabled the language select through the flags on my website: http://photo.eugenios.org/
And I have noticed that for the flag corresponding to Lithuanian language it shows "Luxembourgish / Lietuviškai". When I pressed this flag it switched the language to Luxembourgian.
Somehow I don't seem to have complete language pack installed, so I couldn't check what will happen if I press the flag of Luxembourg.
However making a fast search in Google gave me link to some other person's gallery: http://www.yeralan.org/coppermine/
(don't know which version he is running), which has more language flags displayed, and having same mixed up Lithuanian and Luxembourgian languages.
Btw, I think it should be "Luxembourgian" and not "Luxembourgish" language.
Of course all this can be corrected by users, but I guess it would be better if you fix this in your future updates.