Is the following sentence correct?
The sentence structure in English is fundamentally diferent from French and Spanish
...Or, more precisely, 'from that of French and Spanish'.
I would omit "The" at the beginning, spell "different" correctly and use "in" both times.
Sentence structure in English is fundamentally different from that in French or Spanish.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.