Do thoughts require expression in the form of language,and is it possible to think in the absence of language?
Thoughts do not require expression in the form of language, or in any form of communication at all. Thoughts, by definition, are what occur inside one's mind. Whether the individual experiencing the "thoughts" chooses to communicate those thoughts is entirely up to him or her. And, in the event the individual experiencing the "thoughts" chooses to communicate those thoughts to others, he or she chooses the method of communication, in effect, verbal, written, sign, etc.
Marriage and relationship counselors will always emphasize the necessity of communicating one's thoughts to one's spouse or partner. Everybody -- with the obvious possible exception of those on life-support whose circulatory system continues to function, but whose brain has ceased to function -- experiences thoughts. Relationships disintegrate when one or both parties to the relationship refuse, or are emotionally unable, to orally communicate concerns or grievances to the other.
"Thoughts" are a product of normal brain activity. We experience thoughts in our sleep, in our subconscious, and in our conscious being. Sometimes, knowing when not to express one's thoughts orally or in writing is key to retaining one's position, whether in an organization (e.g., a job, a social group, an athletic team) or in a personal relationship.
Language, whether oral, written, body, or any other form, is a means of communication. Language cannot generally exist without thoughts, but thoughts can and do certainly exist without language.