Adding in the locale data would double the extension size to around 500MB, and adding in the localized help packs would total the extension at around 1 GB.
This is definitely a case where the ability to provide a separate locale or language pack makes sense. Each individual language and help pack would average around 12mb. One can simply download the main extension, and if they want, say, an Italian language and help pack, then one can simply download that separate extension.
The only other feasible way would be to just provide the top three or four languages contained in the main extension. But even that would increase the size by about 50MB, and some folks would feel left out, and with no way to add their own language.
Like it is not feasible to include the huge sound font packages in the timidity extension, as that case too needs to allow a choice of sound fonts, libreoffice needs to be able to provide a choice of languages when it is not reasonable to include them in the package. I will see what I can do, and if it can be done cleanly.