Is "I write these" wrong?
Yes, it must me I write this due to the ini
Pressing the 'ini' revealed 'this', 'these' and 'it' as possible translations. So, you must be right, innit!
What is the past tense of menulis?
there's no conjugation in indonesian language.
However, you could put 'sudah' (already) before the verb when the time is not mentioned.
Saya sudah menulis surat.
(I already wrote the letter)
What is the difference between Itu and Ini?
They are both translated by "this".