How does Yoda's speech sound to native English speakers?
Yoda sounds like a foreigner trying to speak English, but doing a poor job of it. His structure and accent lend it a comical nature.
Per @Lawrence's comment, it is very easy for us to understand Yoda, so that the movies gain the humor, but do not lose comprehensibility.
To me Yoda sounds like someone speaking some English dialect from several hundred years ago. The speech has a sort of Shakespearean feel to it. It doesn't seem "illiterate" or "foreign", just "mystic".