I'm using ModOrganizer2.4.4, so it's rather easy to remove and disable all mods.
0 0 Oblivion.esm
1 1 DLCShiveringIsles.esp
2 2 DLCHorseArmor.esp
3 3 DLCOrrery.esp
4 4 DLCVileLair.esp
5 5 DLCMehrunesRazor.esp
6 6 DLCSpellTomes.esp
7 7 DLCThievesDen.esp
8 8 DLCBattlehornCastle.esp
9 9 DLCFrostcrag.esp
10 a Knights.esp
11 b Correctif.esp
12 c CorrectifSI.esp
13 d Tamriel.esp
14 e Correctif BattlehornCastle.esp
15 f Correctif SpellTomes.esp
16 10 Correctif Knights.esp
17 11 Correctif MehrunesRazor RP.esp
18 12 Correctif ThievesDen RP.esp
19 13 Correctif VileLair RP.esp
20 14 Correctif ThievesDen - SSSB.esp
21 15 Correctif Frostcrag RP.esp
22 16 Correctif HorseArmor RP.esp
23 17 Teleportation Spell.esp
24 18 Enhanced Water.esp
25 19 Correctif Orrery RP.esp
26 1a ImprovedSigns.esp
27 1b Alluring Potion Bottles v3.esp
28 1c Alluring Wine Bottles.esp
29 1d Immersive Weapons.esp
30 1e WeightLifter.esp
31 1f MoreMagicka.esp
32 20 EVE_StockEquipmentReplacer.esp
33 21 EVE_KnightsoftheNine.esp
34 22 Unlimited Rings 1.0.esp
35 23 Unlimited Amulets 1.0.esp
36 24 Dynamic Map.esp
37 25 HUD Status Bars.esp
38 26 Practical Training.esp
39 27 MiniMap.esp
40 28 JG Elven.esp
41 29 Glowing Fractured Soulgems.esp
42 2a Bag of Holding.esp
43 2b Borderless Cyrodiil.esp
but as I said, even with only Oblivion.esm and nothing added to data folder, voice is still german ... btw, I play in French, so this is why i'm guessing it's a wrong voice file/folder for this specific NPC. as i said, still an issue with mod list empty. If you know what folder and file names are related to this NPC in the BSA files, I may be able to find them elsewhere !