Question

1. I will have thought Spanish for ten years by 2018.
2. I will have thought Spanish for ten years in 2018.
(Can we use both prepositions?)

3. He will have gone to Rome when you come next month.
4. He will have gone to Rome if you come next month.
5. He will have gone to Rome by the time you come next month.
6. He will have gone to Rome by next Sunday.
(Can we use all the senteces? Are all grammatical?)

Answer 1

3, 4, 5, and 6 are all correct and usable, yes.

I don't understand 1 or 2.

Answer 2

Thank you. I corrected errors.

1. I will have taught Spanish for ten years by 2018.
2. I will have taught Spanish for ten years in 2018.
(Can we use both prepositions?)

Answer 3

Yes.