Great initiative! I will also add some proposals:
• Racing:
<< Rapido et Furioso >>
<< Buzz l'éclair >>
<< Onde de choc >>
<< Leader >>
<< Scélérat >>
• Defilante:
<< Paysagiste >>
<< Héro >>
<< Logisticienne >>
<< Souris obstinée >> (pour les 100 000 points)
<< Pleine d'espoir >>

Racing:

<< Guepard >>

<< Already in the hole >>

<< Imposible to catch up >>

Defilante:

<< Not falling >>

<< I'm flying! >>

<< Never give up >>

Racing

Belong to Podium
Addict
Ranker
Leader
Best of All Time
Full Speed
the Speed Engine
Checkered Flag
Here I Come
Run That Race
Catch me
On Your Left

Defilante

Long-Suffering

Burlador - Racing
McQueen - Racing
Captain speed - Racing
On point! - Defilante

Prodigy for Racing

Racing
« Barry Allen » (or « Mouse Allen » ??)
« Presto »
« Supersonic »
« Velocity »
« McQueen »
« Quicksilver »
« Hermes » (Greek God of Speed) or « Nike » (Greek Goddess of Victory/Triumph/Speed)

Défilante
« Aficionado »
« Prevailer »
« Hoarder »

I tried picking titles I haven't seen already, like Cheetah lol

De desfilante me gustaria delphilante o como se llame la tipa de village puntuacion maxima El veloz super salto etc (tengo mala imaginacion para esojsjsjs) ee el pro

Racing

<< FAST AS - BOI >>

<< Faster Than Seconds >>

<< ¯\_(ツ)_/¯ >>

<< Use your wings >>

<< Think Faster >>

Defilante

<< You never know >>

<< No fears >>

<< I'm not falling >>

<< Don't look down >>


xD hope that some of my titles made you smile

Defilante:
« Light Footed »
« Tiptoe »
« Dash »
« Point Pursuer »
« Against All Odds »
« Missed Me! »
« Marathoner »
« Coin Collector »
« Platformer »
« On Path »

Speedy
Speed'o Mice

:D

«Aigrefin»
«Ascète»
«Contempteur»
«Souris harassante»
«Véloce»
«500 miles»

Defilante

«Fast and Smart»
«Careful, Fast & Smart»
«Run or Disappear!»
«Don't wait, neither be late»
«Until last plus one»
«Defilante Lover»
«Maximum Concentration»
«My Way!»
«Nice Moves» / «NICE MOVES!»
«Skip, Skip & Run!»

Racing:
«Speedster»
«Speed of Sound»
«Fast Mode»
«Godly»
«Master»
«Can't Touch Me»
«Too Fast»
«Undefeated»
«King/Queen»
«Go, Go!»
«Firework»
-------------------------
Defilante:
«Points Matter Most»
«No Stopping Me»
«Worthy of Points»
«Points King/Queen»

for racing:
<<I am speed>>
<<Invisible>>

for defilante:
<<OWO>>
<<Gotta go fast>>
<<Oof>>
<<Last second!>>

Racing:
<< Race Master >>
<< Black belt >>
<< Try to reach me! >>
<< First of all >>
<< Asphalt King >> // << Asphalt Queen >>
<< Kung Fu Mouse >>
<< Podium first >>
<< Furious >>
<< MY TROPHY! >>
<< Winged Mouse >>
<< Leaving dust >>
<< In a hurry >>

Defilante:
<< In the rhythm >>
<< One more point! >>
<< Just in time >>
<< Maximum score >>
<< Super Mouse Bros >>
<< Mighty Mouse >>
<< Game show >>
<< Electric Mouse >>
<< Its me, mouse! >>
<< I arrived! >>
<< Punctualist Mouse >>
<< Dynamic Mouse >>

Defilante:

One Up!
Spring Mouse
Shortcutter
Defying Gravity

«Speedrunner» for Racing
«Limitless Speed» for Racing/Defilante
«OUCH!» for Defilante
«Cheetah Spirit» for Racing/Defilante
«Mouse-Bolt» for Racing
«Road Runner» for Defilante