Is This Sentence Correct?

The only problem with what you have written is that people will cling to it like a lifebelt, and abandon the sentences with only one meaning, so that ผมจะสอนถาษาอังฤษคุณ for 'I will teach you English' will be considered wrong.

As for 'I will teach English for you'. What is the correct way of saying that? I feel that สอนภาษาอังฤษแทน should appear somewhere.

Let try an experiment. I am sure most people know that in real life conversation we often left words out. What the sentence actually mean will have to be deduced from context. So those three sentences can be shorten to

จะสอนภาษาอังกฤษให้

จะสร้างบ้านให้

จะขับรถให้

Who is the subject and who is the object in each sentence will have to come from context. Now, if we try to reduce the sentence down further by taking preposition off. We would have

จะสอนภาษาอังกฤษ (I, he,she, etc) will teach English

จะสร้างบ้าน will build house

จะขับรถ will drive car

Without the pp to suggest that there are objects, those sentences' meanings have changed. If we try to put the object back we would get

จะสอนภาษาอังกฤษคุณ (I, he,she, etc) will teach you English

จะสร้างบ้านคุณ will build your house

จะขับรถคุณ will drive your car

The latter two sentences now contain structure Noun(รถ,บ้าน) +Pronounce(คุณ) which is shorten form of Noun+ของ+Pronounce. They are used to show procession and interpreted as such on those two sentences.

To do the same on the first sentence and interpret it as "will teach your English" would be illogical. That is why Thai perceived them as "Will teach you English.

Make sense?

I think that the interesting thing for me is to compare the RID with what people say. ให้ has taken on a meaning all of its own. The difference between สร้าง and สอน is that สอน can have two objects สอนหนังสือ สอนคุณ and this is most likely the reason that the RID decided to give guidence on how to use it in a sentence. Amost universally ignored, in speech.

Conversation doesn't matter as far as meaning goes because it can always be clarified and if not the speaker can deny it, noone records it. Also the situation to which the words apply is clear, writing is different; it is best not to leave out vital words, but it is just as easy to add superfluous words.