"We are having dinner with Duo."
Translation:Duo ile akşam yemeği yiyoruz.
"Biz Duo ile akşam yemeği yiyoruz" must be accepted as well. Even we don't use subjects too much in Turkish, it is not wrong,is it?
Why is it ''Duo'yla'' and not ''Duo'ylu''. Isn't it 4-way vowel harmony, not 2? Because of ''tuzlu''?
I think <instrumental case> uses 2-way harmony ( (y)la , (y)le ), but <With> (Adjective Formation) uses 4-way harmony (lü, lu, li, lı).
Just adding to what ArdaS_H already said, they are different things. tuzlu, şekerli are adjectives, they mean smth like "salty, sugary" (but in this course they're translated as "with salt, with sugar" because english can't use that mechanism for all words). so their -lu, -li suffixes aren't the shortened "ile" suffix meaning "with", they're the suffixes for adjective formation (lü, lu, li, lı)