I'm not aware of any place that sell Primo/NextGen on SD card that would work with your unit. Most chinese units don't license Primo/NextGen from NNG. They take (steal) software and installed it on their unit and sell the unit not the software.
All of the eng-*-lua files are not TTS capable so you can ignore them. If you don't hear any voice when selecting the others voice file (like tts-andr+4.3-4.4) then your unit is NOT capable of TTS. This could be because they didn't install a TTS engine such as Google, Pico, VocalizerEx, SVOX, etc... on it.