Created attachment 113755 [details]
comparison between DejaVu and correct Lao fonts
In Lao script, there are vowels that are written on top of consonants and tone markers which are written on top of consonants as well. In the case that a consonant contains a top vowel and a tone marker, the tone marker should be placed a little bit higher because it is otherwise displayed at the same position where the vowel is shown. If it is not done, it could get impossible to read/understand the word (although I do not have an example because I am no native speaker in Lao language).
DejaVu includes the lao characters but does not take into account the problem that I have explained above. I am running a Ubuntu without special configurations in my fonts and it seems to me that DejaVu is more or less the only font that supports Lao characters in a default installation. Therefore, it is the fallback-font for nearly every text written in Lao language.
To clarify the problem that occurs, I have written a short piece of text which compares the result of Lao script for DejaVu and two Lao fonts (Phethsarath and Saysettha). So the result should look more or less like the one that Phethsarath and Saysettha produce.
Thai language/script, which is very similar to Lao, has the same "feature". By default, it works in an Ubuntu installation. Maybe, it is possible to get the idea how to implement this behaviour by inspecting a free Thai font?
If there are any more questions or if I could help with further information regarding Lao script, please feel free to contact me.