I noticed that on my HTC, going to Settings -> Accessibility Options -> Output speech -> speech synthesis engine Google, there 's the "Install Voice Data"
I do not know if this option is present only in HTC phones, but it would be possible, if the language is not installed, open this setting to allow you to download the required language?
You can install voice engines and voices from Google Play and then select an engine in the settings. You can try svox or ivona.
It's not specific to HTC but part of Android.