他和你用哪种语言谈话?
"他和你用哪种语言交谈?"
'交谈' is better than '谈话' because '交谈' means 'talk to each others; while '谈话' mainly means 'speak' or 'talk'.
You can speak or talk by yourself, but you cannot having a conversation on your own.
学习语言的时候有什么困难?
No problem above
一个孩子每天多长时间应该练习语言?
"一个孩子每天应该花多长时间练习语言?"
Better add an verb '花'(spend) here
一个儿童可以说几种语言?
No problem above
你哪种语言应该学习?
You are placing the [object] directly after the [subject ]
It is better to place the verb '学习'directly after the subject '你'
- "哪种语言你应该学习?"
- "你应该学习哪种语言?"
你的父母会什么语言?
No problem here
你未来想不想学习一种新的语言?
你将来想不想学习一种新的语言?
Should replace '未来' with '将来' for the meaning of: "in the future" because '未来' itself is a noun or an adjective for 'future'