@clavadys
Read this thread [Only registered and activated users can see links. ] (Don't be put off by "American English" in the thread title, it's the same problem regardless of Language used. Read the first post there thoroughly). In brief, you need to have the full EU mapping for Voice Command to work, converting the device won't change that requirement. You may simply put the rest of EU on a microSD rather than on the internal device memory with EU South however make sure you use the same type (NTU in your case) and same map version.

However unless you buy the official maps from Garmin legally, ASR still won't work even with the correct additional ASR & SRD files sourced and loaded appropriately. That's because your DS61 (HWID 2588) has protected firmware with strong MSV (Map Signature Verification). Therefore the use of "unofficial" (i.e. unlocked) maps will trigger an onscreen message "Maps are corrupt and cannot be used".

We cannot help you with patching the firmware here because that's against forum rules now (being in breach of Garmin's EULA). Google around for "Universal Firmware Patcher" if you want to go down that path. If you do buy the maps legally, Garmin still won't give you any additional ancillary files and that includes the ASR/SRD files. You'll have to find them elsewhere too if you don't have what you need already supplied with the EU Sth mapping.