Same or similar pronunciation is not unique to any language. The words cannot be interchanged nor do they come close to meaning.

"then" is used in the context of timing or sequence. "Do this first then that" "I went to the movie then I went to the restaurant"

"than" is used in the context of comparison, choice and preferences. "A is larger than B". "I'd prefer to go to a movie than to go to a concert"