טקסט מקורי - אנגלית - The language being taught

Is this sentence correct? isn't it: ... in the 'original' language must be ...

I don't know, my english is not fluent. This is what I wanted to say :

For example, you have a french lesson commented in english :
« "Bonjour" means "Hello" »
If you want to translate the lesson into italian it will be :
« "Bonjour" significa "Buongiorno" »

In this example the french language is the taught language and the english and spanish languages are the languages used to comment the lesson. "Bonjour" is kept untranslated. Does it sound right to you?

That part is correct, but the sentence structure is not quite right. It should be like this:

When translating a language course, be careful to keep the parts written in the language being taught untranslated!

Or simpler still:

When translating a language course, be careful not to translate the words written in the language being taught!

CC: cucumis