PLAY_PED_AMBIENT_SPEECH_NATIVE

Here's a list of most of the in-game voice-lines: https://raw.githubusercontent.com/femga/rdr3_discoveries/refs/heads/master/audio/audio_banks/audio_banks.lua

speechParamHash can be found here: https://github.com/femga/rdr3_discoveries/tree/master/audio/audio_banks ("speech_params_force" seems to work best)

Text indented on the left such as "0008_S_F_M_ISPWORKER_01_BLACK_02" is the dictionary_name, the strings underneath is the index_name.

index_name with a number (E.G _01, _02, _03 etc..) are just extra voice lines, most voice lines seem to works best without the added '_01' on the end  

Here's the following setup I was able to create for playing voice lines through your Player (this of course can be changed to be used for other Peds)

struct ScriptedSpeechParams {
    const char* IndexName;
    const char* DictionaryName;
    alignas(8) int variation;
    alignas(8) Hash speechParamHash;
    alignas(8) Ped listenerPed;
    alignas(8) BOOL syncOverNetwork;
    alignas(8) int v7;
    alignas(8) int v8;
};

static_assert(sizeof(ScriptedSpeechParams) == 0x40, "incorrect ScriptedSpeechParams size"); 
       
void play_npc_voice(Entity npc, const char* dictionary_name, const char* index_name) {

    // set the ScriptedSpeechParams struct as you wish
    ScriptedSpeechParams params;
    params.IndexName = index_name;
    params.DictionaryName = dictionary_name;
    params.variation = 0;
    params.speechParamHash = RAGE_JOAAT("speech_params_force");
    params.listenerPed = PLAYER::PLAYER_PED_ID();
    params.syncOverNetwork = true;
    params.v7 = 1;
    params.v8 = 1;

    AUDIO::PLAY_PED_AMBIENT_SPEECH_NATIVE(npc, (Any*)&params);
}

example of use:

play_npc_voice(npc, "0405_U_M_M_RhdSheriff_01", "RE_PH_RHD_V3_AGGRO");