That's unfortunate. Thanks for the direction.

I opened the account.invoice.form's edit interface... but how I do I add labels in other language? The string='something'? I don't think so...

Depending on your requirements (your description is more than vague), you'll need an experienced Odoo/QWeb developer or the necessary knowledge to do it yourself.

I only want the labels like item name, description, price, total, etc displayed/printed in two languages side by side.

See my amended answer.

Ah, I figured that as well. Another set of rote manual work, what a pain. I do wonder why this isn't a proper feature though, and why you need to create an entire customer entry to produce invoice and bills.

I live in a country with 4 offical languages and to me this seems rather an unusual requirement nevertheless.

Well, my perspective is a little different in that I've seen pen and paper invoices most where the labels are printed in both languages. Then again, it's not exactly my own requirement, just my friend's shop who wants to use Odoo now that tax has been implemented for the first time in the country represented by this flag.