If you want to change the language (or accent), it's a little convoluted:
1. First, go to Settings>Language & Input>Languages, and select the one you want. Make sure it's listed as Default (or move it to the top of the list).
2. Next, go to Settings>Language & Input>Text-To-Speech Output, and tap the gear icon next to Google Text-To-Speech Engine, then Language, and select that language.
3. Go back one menu level, and tap Install Voice Data. Make sure the language data is installed.
Google Maps should now be speaking to you in that language/accent.