I am running osmand 1.5 on cyanogenmod 11 and I solved the problem by installing th english uk male voice pack and setting this as my tts output, when I checked osmand I got a male british voice, I then set the voice output to english uk female and this worked
Google tts settings, install voice data, english uk, then select the voice
The above setting wasn't persistent after a reboot so I set google tts output to US English and then back to UK English and this seems to work, will update with any further issues that I find.
I just found that starting the Osmand+ app with the sound on my device muted it switched to a dreadful scratchy American accent. It seemed stuck that way. Reading the suggestion to switch in android settings to a different language and then back again fixed the problem.