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1. Finally / eventually i went to England in this summer.

2. I cooked dinner last night.

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No, the last one is "Lastly, I cooked dinner." 

"En son akşam yemek pişirdim" or "en son akşam akşam yemeği pişirdim", would give "i cooked (dinner) the last night".

mltm is right.

It might be "Lastly, i cooked dinner". Sorry for my fault and thanks for correction.

Well, guys please don´t take it as a correction but my way of translating it:

2. It was a dinner´s meal when I cooked last time.

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you are right in your thinking but I think what I said is more or less the same thing because the question is "what did you cook the last time you cooked", "Lastly I cooked dinner"

-en son ne pişirdin?

-en son akşam yemeği pişirdim.

so we can say

- (en) sonunda = at last

- "en son" or "son olarak" = lastly

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