Position of direct object in a sentence with an adverb of degree
So, does the usage of an adverbial expression (the 得- construction) require the direct object to be placed elsewhere, before the subject? &quot;他说法文说得那么好&quot;, but &quot;法文他说得那么好&quot;?

They are two different topics in a [(topic) + (comment)] sentence.
[他说法文 (topic)] + [说得那么好 (comment)]
说得那么好 is the comment on the topic 他说法文
On the topic of 'he speaks French', the comment is 'speaks very well'
~
[法文 (topic)] + 他说得那么好 (comment)]
他得说那么好 is the comment on the topic 法文
On the topic of 'French', the comment is 'he speaks very well'
~
[subject + V + 得 + adjective] doesn't always require an object
Example: 他跑得很快
When there is an object, the object can be placed before the subject as a topic.
Example: 中文 他學得很快
When an object is placed after the subject and verb, it becomes a [SVO] sentence (e.g. 他學中文) and the sentence can be the topic.
Example: 他學中文 學得很快