Solving a grammar in Accountant way. ??
1. The official language of Morocco is Arabic, but Spanish and French are widely understood in addition to

2. The official language of Morocco is Arabic, but Spanish and French are widely understood as well

As accountant, I had known about main product and by product, I tried to use it to solve the problem i.e which sentences are correct?

"As well as" is match with main product and "in addition to" is by product.

When I talked to both of something that equal (main product) , such as Arabic and Spanish and French, I should use "as well' instead of "in addition to"

So, the sentence #2 is correct.

Is it logic?

Question

Solving a grammar in Accountant way. ??
1. The official language of Morocco is Arabic, but Spanish and French are widely understood in addition to

2. The official language of Morocco is Arabic, but Spanish and French are widely understood as well

As accountant, I had known about main product and by product, I tried to use it to solve the problem i.e which sentences are correct?

"As well as" is match with main product and "in addition to" is by product.

When I talked to both of something that equal (main product) , such as Arabic and Spanish and French, I should use "as well' instead of "in addition to"

So, the sentence #2 is correct.

Is it logic?

Answer

I don't follow your accountant logic, but #2 is correct. You can't end a sentence with "in addition to".

So #1 can be rewritten with "in addition to" and without "but":
- In addition to Arabic, the official language of Morocco, Spanish and French are widely understood.

Or you can use the more natural "also", which gives this nice clean syntax:
- The official language of Morocco is Arabic, but Spanish and French also are widely understood.

Answer

Yes.  You cannot use the "addition to" with out the object to which you are adding it  - if you see what I mean.   
You could say: 
In Morocco, Spanish and French are widely understood, in addition to the official language of Arabic.  
In Morocco, in addition to the official language of Arabic, Spanish and French are also widely understood. 
In addition to the official language of Arabic, Spanish and French are also widely understood in Morocco.
Both are correct, though they are both a little awkward.