Remi_Brun_-blablabla_blalala-ASpi777XisA.en.vtt
Remi_Brun_-not_important_but_here_to_nag-ZIBcQ5tMB2U.en.vtt
Remi_Brun_-still_here,just_deal_with_it!-hOxG4g05z4w.en.vtt
...

(Remi_Brun)(_.+)([a-zA-Z0-9-_]{11}.fr.vtt)

Remi_Brun-ASpi777XisA.en.vtt
Remi_Brun-ZIBcQ5tMB2U.en.vtt
Remi_Brun-hOxG4g05z4w.en.vtt
...

rename 's/(Remi_Brun)(_.+)([a-zA-Z0-9-_]{11}.fr.vtt)/$1-$3/' Remi*