Why is Matthew 17:21 missing or only a footnote in my Bible?

Matthew 17:14-21; Mark 9:29; Luke 9:37-43

Why is verse 11 missing in Matthew 18?

Matthew 18:11

Are some things lost when the Bible is translated into other languages?

Nehemiah 8:8

Should verses 9-20 be included at the end of Mark 16?

Mark 16:9-20