*beep* engage pedantry mode... Videtur (yeah, the present case has an e, no big deal) means either: "seems" or "is looked at (upon)." If it is "looked upon," then "highly" would be an adverb... Thus, "alte." If it is to be "seems," then it would in fact be the neuter subjective - "altum." Assuming the least amount of spelling errors in the original text, it would more correctly translate into

"Whatever is composed in Latin, seems noble."

Exit pedantry mode. Anyone more knowledgable than I, please, correct me, and contribute to the Latin education of Everything.