"省略中间的音节" can be translated into English as "omit the middle syllables" or "elide the middle syllables".
"Omit" means to leave out or fail to include something.
"Elide" has a similar meaning in this context, referring to the omission of a sound or syllable in speech or pronunciation.
Both expressions are appropriate, but "omit" might be more commonly used in general contexts, while "elide" could be more specific to linguistic or phonetic discussions.