Why is English in instrumental case? Is it not supposed to be in Accusative case?
"To speak some language" requires instrumental (think of it as of using language as a tool)
Isn't англійський a masculine noun? The tip & notes said that ю is used for feminine nouns in instrumental case.
Англійський is a masculine adjective.
Here we can see an example of nominalization: instead of англійська мова (English language) we commonly say just англійська (українська, німецька,...) - just like in English. After the nominalization the adjective keeps the gender of the noun it used to be an attribute of: мова - feminine.
Дякую ще раз, Vinnfred! Your explanation cleared up one of my biggest questions concerning case endings.
I've also heard "Ви розмовляєте..." used for "Do you speak..." Are they both equally used and correct?
I think they are, because both mean "Do you speak..."?, just "розмовляти" is more like "talk" and "говорити" means literally "speak", but both can be used for "Do you speak...?". In different phrase lists you can find both, but "Ви розмовляєте..." is more common.
I've heard before "Ви говорите по-англійський?" - is this incorrect or just another possible way of saying it?
"По-англійськи", "по-українськи" means more "in english (or maybe England) manner", "in Ukrainian manner". Like in "Котлета по-київськи" - I suppose some of you heard of that. The meaning would be: Like it's done in Kyiv.
We also use a phrase "Піти по-англійськи", wich means "To leave without saying goodbye". But I don't know where did it come from :).
"Говорити по-англійськ-и/-ому" is probably also acceptable, but I wouldn't say that. I would say "Говорити англійською" or "Розмовляти англійською" - it is much better.
At least in Russian it would be correct. See Vinnfred's comment above also.
In Ukrainian you can say "по-англійськи" but that would mean "English style" e.g. food or a style of dressing or doing something.