Basically the huge majority should be changed, the current names for the Celtic units are mostly based on modern Celtic languages (for example modern Welsh).
I made a list of names from my various proposals based on ancient Gaulish or old Celtic languages. Here a summary:
Cingetos. Designate a member of the warrior class, litt. "those-who-walk-in-front".
Catucos. Meaning combatant, from the root Catu-, fight.
Batoros. Meaning "who-hit-hard" or "who-knocks", a fighter.
Ambactos. Meaning "who-is-around", a satellite companion, a client or a servant. Not necessarily a low status since the word evolved in ambassador.
Eporedos. Meaning a cavalryman or a knight. High-member of the warrior-class.
Epossos. Meaning a cavalryman or a knight. High-member of the warrior-class.
Marcacos. Meaning a cavalryman. The word Marcos is a synonym of Epos for the horse but could be used for a different type.
Bagauda. Meaning combatant or bellicose, associated with rural revolts and brigands during the Roman Empire.
Selgos. Meaning hunter.
Telmiuicos. Meaning slinger from a reconstruction based on Telmi- for the sling and Uicos for victorious, which gives litt. "victorious-by-the-sling".
Talmoris. From the Old Breton Talmorion equivalent of the Latin funditoribus, a dative plural word for Slinger.
Bariogaisatos. Meaning "furious spearman", from the word Bario- (angry, furor) and the word Gaisa- (spear).
Adretos. Meaning "who-runs-fast", an attacker.
Comaterecos. Meaning patrician or senator.
Agrocuna. Meaning war-dog or battle-dog. From Agro- (battle) in Gaulish and Cuna (Dog) in Primitive Irish.
Epouanos. Meaning litt. "horse-killer".
Soliduros. Attested word for the bodyguard of the Sotiates' King.
Adscoros. Meaning attendant or retainer.
Uerouicos. Meaning victorious warrior, great fighter, litt. "very-victorious".
Uassos. Meaning servant or serf.
Talanos. Meaning support or supportive person.
Excingos. A attacker or a warrior, litt. "who-get-out-to-fight".
Namantobogios. Meaning "smasher of enemies".
Essedon. Attested word for the chariot in general. Used in the context of war chariot by the Romans.
Argos. Meaning champion or noble.
Caur. Old Irish for champion, same logic than in the Gaulish Cauaros, another word for champion.
Changelog for the current rosters.
[file name] ; [specific name i.e. native language] ; [generic name i.e. English equivalent in game] ; [literal meaning for future reference] ; [used language]
brit_catafalque.xml ; Cassiuellaunos ; Catafalque ; Passionated Leader ; Gaulish
brit_cavalry_javelinist_b.xml ; Marcacos ; Raiding Cavalry ; Horseman ; Gaulish
brit_cavalry_swordsman_b.xml ; Eporedos ; Celtic Cavalry ; Cavalryman ; Gaulish
brit_champion_cavalry.xml ; Essedon ; Celtic Chariot ; Chariot ; Gaulish
brit_champion_infantry.xml ; Argos ; Celtic Champion ; Champion ; Gaulish
brit_hero_boudicca.xml ; Boudica ; Hero Charioteer ; Victorious ; Gaulish
brit_hero_caratacos.xml ; Caratacos ; Hero Swordsman ; Beloved ; Gaulish
brit_hero_cunobelin.xml ; Cunobelinos ; Hero Cavalry Swordsman ; Strong as a Dog ; Gaulish
brit_infantry_javelinist_b.xml ; Adretos ; Skirmisher ; Who-runs-fast ; Gaulish
brit_infantry_slinger_b.xml ; Talmoris ; Celtic Slinger ; Slinger ; Old Breton
brit_infantry_spearman_b.xml ; Catucos ; Celtic Spearman ; Combatant ; Gaulish
brit_ship_fishing.xml ; Longos ; Fishing Boat ; Long Boat ; Gaulish
brit_ship_merchant.xml ; Nauson ; Merchantman ; Ship ; Gaulish
brit_ship_trireme.xml ; Pontos ; Medium Warship ; Ship ; Gaulish
brit_siege_ram.xml ; Molton ; Battering Ram ; Ram ; Gaulish
brit_support_female_citizen.xml ; Bena ; Celtic Woman ; Woman ; Gaulish
brit_support_healer_b.xml ; Druid ; Healer ; Wise ; Gaulish
brit_support_trader.xml ; Uogition ; Trader ; Carrier ; Gaulish
brit_war_dog_b.xml ; Agrocuna ; War Dog ; Battle Dog ; Archaic Irish
gaul_catafalque.xml ; Ambiorix ; Catafalque ; King in All Directions ; Gaulish
gaul_cavalry_javelinist_b.xml ; Marcacos ; Raiding Cavalry ; Horseman ; Gaulish
gaul_cavalry_swordsman_b.xml ; Eporedos ; Celtic Cavalry ; Cavalryman ; Gaulish
gaul_champion_cavalry.xml ; Uerouicos ; Gallic Noble Cavalry ; Victorious Warrior ; Gaulish
gaul_champion_fanatic.xml ; Bariogaisatos ; Naked Fanatic ; Furious Spearman ; Gaulish
gaul_champion_infantry.xml ; Soliduros ; Celtic Champion ; Champion ; Gaulish
gaul_hero_brennus.xml ; Brennos ; Hero Swordsman ; Commander ; Gaulish
gaul_hero_vercingetorix.xml ; Uercingetorix ; Hero Cavalry Swordsman ; King of the Great Warriors ; Gaulish
gaul_hero_viridomarus.xml ; Britomaros ; Hero Spearman ; With Great Discernment ; Gaulish
gaul_infantry_javelinist_b.xml ; Adretos ; Skirmisher ; Who-runs-fast ; Gaulish
gaul_infantry_slinger_b.xml ; Talmoris ; Celtic Slinger ; Slinger ; Old Breton
gaul_infantry_spearman_b.xml ; Catucos ; Celtic Spearman ; Combatant ; Gaulish
gaul_ship_fishing.xml ; Longos ; Fishing Boat ; Boat ; Gaulish
gaul_ship_merchant.xml ; Nauson ; Merchantman ; Ship ; Gaulish
gaul_ship_trireme.xml ; Pontos ; Medium Warship ; Ship ; Gaulish
gaul_siege_ram.xml ; Molton ; Battering Ram ; Ram ; Gaulish
gaul_support_female_citizen.xml ; Bena ; Celtic Woman ; Woman ; Gaulish
gaul_support_healer_b.xml ; Druid ; Healer ; Wise ; Gaulish
gaul_support_trader.xml ; Uogition ; Trader ; Carrier ; Gaulish