Problem with foreign language characters

Im using Lithuanian language, it has such letters as ą,č,ę,ė,į,š,ų,ū.
When I format pdf, instead of this letters I see a[], c[], e[] and so on.
The strange things, that some of the letters are shown correctly, some not.
Also interesting thing – I installed the same plugin to different website with Lithuanian language, and added the same field names, ant there in pdf it is shown correctly. What could be the problem here?