I've been getting this strange bug where my Blunt and Restoration skills, as well as my spells give German (or mix German-English) descriptions when highlighted. Here's a list of my mods + Races Rebalancing mod:

Oblivion.esm
Windfall.esm
Francesco's Leveled Creatures-Items Mod.esm
Francesco's Optional New Items Add-On.esm
Oscuro's_Oblivion_Overhaul.esm
Mart's Monster Mod.esm
Mart's Monster Mod for OOO.esm
FCOM_Convergence.esm
Armamentarium.esm
Artifacts.esm
TantrivayliaChimer.esm
Unofficial Oblivion Patch.esp
UOP Vampire Aging & Face Fix.esp
Oblivion Citadel Door Fix.esp
DLCShiveringIsles.esp
Unofficial Shivering Isles Patch.esp
Francesco's Optional Chance of Stronger Bosses.esp
Francesco's Optional Chance of Stronger Enemies.esp
Francesco's Optional Leveled Guards.esp
FCOM_Francescos.esp
FCOM_FrancescosItemsAddOn.esp
FCOM_FrancescosNamedBosses.esp
Fran_Lv30Item_Maltz.esp
DLCHorseArmor.esp
DLCHorseArmor - Unofficial Patch.esp
DLCOrrery.esp
DLCOrrery - Unofficial Patch.esp
DLCVileLair.esp
DLCVileLair - Unofficial Patch.esp
DLCMehrunesRazor.esp
DLCMehrunesRazor - Unofficial Patch.esp
DLCSpellTomes.esp
DLCSpellTomes - Unofficial Patch.esp
LSB Skull Weapons (Clean).esp
Mage Equipment.esp
DLCThievesDen.esp
DLCThievesDen - Unofficial Patch.esp
DLCThievesDen - Unofficial Patch - SSSB.esp
Slof's Oblivion Robe Trader.esp
Oblivion WarCry.esp
Oblivion WarCry EV.esp
FCOM_WarCry.esp
Oscuro's_Oblivion_Overhaul.esp
OMOBS_SI.esp
ArmamentariumArtifacts.esp
Mart's Monster Mod - Additional Enemy NPC Vars.esp
FCOM_Convergence.esp
FCOM_EntropicOrderRebalance.esp
FCOM_RealSwords.esp
Mart's Monster Mod - More Wilderness Life.esp
Mart's Monster Mod - Extra Wounding.esp
Mart's Monster Mod - Safer Quest Locations.esp
Mart's Monster Mod - Dungeons of MMM.esp
Mart's Monster Mod - Farm Animals.esp
Mart's Monster Mod - Diverse WaterLife.esp
Mart's Monster Mod.esp
ArmamentariumLL4OOO.esp
ArmamentariumLLMagicOOO.esp
KDCircletsOOOOptimized - Loot Only.esp
Mage Equipment - OOO.esp
Artifacts.esp
Artifacts - ArmaCompleteAddon.esp
GlenvarCastle.esp
Malevolent.esp
Tantrivaylia.esp
VHBloodlines 1.2.esp
Windfall.esp
DLCBattlehornCastle.esp
DLCBattlehornCastle - Unofficial Patch.esp
DLCfrostcrag.esp
DLCFrostcrag - Unofficial Patch.esp
Knights.esp
Knights - Unofficial Patch.esp
TOTF.esp
MannimarcoRevisited.esp
MannimarcoRevisitedOOO.esp
Mart's Monster Mod - City Defences.esp
FCOM_Knights.esp
Moriarcis.esp
Quest Award Leveller.esp
Quest Award Leveller - Battlehorn Castle.esp
Quest Award Leveller - Vile Lair.esp
Quest Award Leveller - Mehrunes Razor.esp
Quest Award Leveller - Knights of the Nine.esp
bgMagicEV.esp
bgMagicSpellTomes_for_WryeBash.esp
bgMagicItemSigil.esp
bgMagicEVStartspells.esp
bgMagicEVAddEnVar.esp
bgMagicEVPaperChase.esp
bgMagicPotionNumberSoulGemValue.esp
bgIntegrationEV.esp
bgMagicEVShader.esp
bgMagicLightningbolt.esp
SupremeMagicka.esp
SM_ShiveringIsles.esp
SM_DLCSpellTome.esp
SM_OOO.esp
SM_MMM.esp
SM_EnchantStaff.esp
SM_Scrolls.esp
SM_SigilStone.esp
bgMagicEV_Conjuration_for_Supreme_Magicka.esp
MidasSpells.esp
OOO-Level_Stock.esp
bgBalancingEVCore.esp
Bashed Patch, 0.esp
TJBUniqueMagesStaffs.esp

Any ideas on what could be causing the language issue?

Pretty sure Oblivion WarCry.esp is the German version of the one you already included and could be removed.

I dunno, but here is some random LO advice.

-- UOP Vampire Aging & Face Fix.esp
Deprecated. Use Wrye Bash's Bashed Patch for that.

-- Oblivion Citadel Door Fix.esp
Only use when really neccessary.

-- TJBUniqueMagesStaffs.esp
Bashed Patch always goes last.