Correct spelling


Correct spelling, explanation: the adjective international is the base word here, while the suffix added to change it into an adverb is -ly. The adverb suffix is always -ly and there are no instances where it’s different so in order to create an adverb it has to be added. So on top of the ending l of international it forms the only correct version of the word: internationally.

Definition of internationally:
1. Across many nations in the world.
TOEIC is an internationally approved and respected English proficiency exam.
The shipment for this product is available both locally and internationally.

Incorrect spelling


Incorrect spelling, explanation: the word internationaly instinctively seems like it’s lacking something. When you know that the base word is international, the sole y at the end seems out of place and unclear. It’s not until you add the other l, and form a full and proper suffix -ly, that the adverb becomes understandable.