1. Mattie's first wish came true in 2001.

2. Mattie's first wish was realized in 2001.

(Are both the same?)

in 2001
3. in two thousand one
4. in twenty one.
5. in twenty o one.
(Which reading is OK? Do you have other kinds of reading?)

Both sentences mean the same thing. In writing, we never BEGIN a sentence using numerals, but within the sentence, it's best to use them if it takes a lot of words to spell it out. In this case, 2001 is correct in writing the sentence. And, in speaking, we would say two thousand one.

1. Yes, both sentences convey the same meaning. Both "Mattie's first wish came true in 2001" and "Mattie's first wish was realized in 2001" indicate that Mattie's first wish was fulfilled in the year 2001.

2. Out of the options you provided for expressing the year 2001, the correct reading is "in two thousand one." This is the conventional and widely accepted way to pronounce the year 2001. The other readings you mentioned, such as "in twenty one," "in twenty o one," are less common and could potentially cause confusion or misinterpretation.

Regarding other kinds of reading, there are no specific alternate readings for the year 2001. However, in general, there can be alternative pronunciations for numbers in certain contexts. For example, "1,234" can be read as "one thousand, two hundred thirty-four" or alternatively as "twelve hundred thirty-four." The context and preference of the speaker usually determine the appropriate reading.