<lang_en>Hello</lang_en>
<lang_it>Ciao</lang_it>
... some stuff that doesn't need to be translated ...
<lang_en>Goodbye</lang_en>
<lang_it>Addio</lang_it>
etc etc
If you want to add a translation for e.g. French, open the .txt file with your favourite editor and add:
<lang_fr>...</lang_fr>
Below the <lang_it>Ciao</lang_it> line.
Caveats: