Thank you for your help.
1. He will have gone to Germany this Sunday.
2. He will have gone to Germany by this Monday.
(Do you mean both are grammatical?)
3. You will have lost the ring this July.
4. You will have lost the ring by this July.
(Are both grammatical?)
5. I shall have read the letter three times if I read it again.
6. I will have read the letter three times if I read it again.
(Can we use both 'will' and 'shall'?)
1. No
2. Yes
3. No
4. Yes
5. Yes (British-English)
6. Yes (American-English)