Learn English – Is ‘much better’ correct usage?

The term is extraposition, but for that make sense, I need to correct some of your parsing.

The key construction here is "so […] that […]". For example:

The snow was so soft that our shoes sank down pretty nearly to the walk. [link]

The horses are beaten so hard that the tassels from the whips became imprinted on their memories, said Edgar. [link]

It was just so much fun that it made up for the frustration that might have been. [link]

So is an adverb modifying an adjective such as soft, an adverb such as hard, or a determiner such as much. The that-clause serves as a "complement" to so: it completes the meaning. (The word that itself, by the way, can frequently be omitted without changing the meaning; hence "I was so happy I sang all day" [link], where "I sang all day" is still a that-clause, despite the lack of a literal that.)

Now, returning to your sentence:

So much is at stake that courses in foreign languages are often inadequate training grounds, in and of themselves, for the successful learning of a second language.

The subject of this sentence is:

so much / that courses in foreign languages are often inadequate training grounds, in and of themselves, for the successful learning of a second language

and the predicate is:

is at stake

("How much is at stake?" "So much, that courses in foreign languages are often inadequate training grounds, in and of themselves, for the successful learning of a second language!")

As you can see, the that-clause, even though it's part of the subject, has been separated from the rest of the subject, and put after the predicate. This is called extraposition: the that-clause is extraposed (extra- = "outside", posed = "put, positioned, located").

Too much modifies a noun, a verb, or an adverb, and much too modifies an adjective or adverb.