My Spanish is weak, at best. But I like the legroom of an exit row. Does Avianca really limit exit row seats to Spanish speakers?
Officially you need to be able to speak "Spanish or English" to sit in the exit row in general, or Spanish to sit in the window seat of an Exit Row.
However despite this being their official policy, there are multiple reports of people being removed from exit row seat (including non-window seats) if they do not speak fluent Spanish. I can't comment on how frequently this occurs for non-Window seats.
If you only speak basic Spanish (and at least reasonably good English) I would suggest selecting either an aisle or middle seat in the Exit Row and, at least based on their policy, you will be fine.