RGNVoiceEditor. Current version is v1.04. You can find it here:

Code:
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Here's how to use it:

0. Download RGNVoiceEditor v1.04+ from the link above.

1. Click the Open button and select your GCD or RGN firmware. This must be the proper TWN firmware modified for your HWID gps. If you have no clue what I am talking about, read the thread about the TWN firmware from the link above.

2. You should see a list of supported voice on the left side. On the right side, you can select the new voice you want to add. Do not change the English_American_ voice.

3. For each voice you select in step 2, you need to convert it to make it compatible with the TWN firmware. Click the button to select a US-firmware-type voice and to convert it to TWN firmware. the suffix 'twn' will be automatically added to the modified file. We'll talk about this later.

4. You need to save the modified firmware with the new voice. Click the Save button. The new firmware will be saved as RGN.

5. You are nearly done. You need to flash your GPS with the new firmware. If you do not know how, you should probably go and watch TV. This is not for the weak of heart. Read also all about it in the TWN firmware thread with the link above.

6. Copy the modified VPM file to your GPS. Make sure to remove the 'twn' suffix I added to the file. It needs to have the original name when put on the GPS.

turbocc RGNVE1

Official disclaimers:

*** Do this at your own risks! ***
*** Do not flash any FW if you are getting weird errors ***
*** Do not use RGNVoiceEditor if you did not make the TWN firmware work prior to using this program ***


Known bugs: I think the new voices will appear under the previous voice name. If you replaced the Fukein__ voice for the Russkiy__ voice, you may find it under the Fukein__ name.

via turboccc GpsPasSion


update in post 20, thanks turboccc