Due to the principles of processing fluency (also known as cognitive fluency, discussed here many times before), we know that information that is easier to process is perceived to be–among other features–more familiar, pleasant, truthful and less risky.
A recent study has shown that this is also true for foreign accents: statements spoken by non-native speakers are perceived to be less trustworthy, even if their accent is mild:
Non-native speech is harder to understand than native speech. We demonstrate that this “processing difficulty” causes non-native speakers to sound less credible. People judged trivia statements such as “Ants don’t sleep” as less true when spoken by a non-native than a native speaker. When people were made aware of the source of their difficulty they were able to correct when the accent was mild but not when it was heavy. This effect was not due to stereotypes of prejudice against foreigners because it occurred even though speakers were merely reciting statements provided by a native speaker. Such reduction of credibility may have an insidious impact on millions of people, who routinely communicate in a language which is not their native tongue.
via Mind Hacks