Languir means 'to languish' or 'to pine', conveying a sense of longing and suffering due to delay or unfulfilled desire. It's a more evocative and less common word than simply 'waiting'.
In the song, Colonel Reyel sings, "Arrête de me faire languir" (Stop making me languish/pine). He uses this word to express his intense impatience and desire for his love interest to let him in, highlighting the emotional torment of being kept at a distance.
Colonel Reyel's "Laisse-moi Entrer" is a super direct and passionate plea from someone who is absolutely smitten and ready to commit! He's been knocking on this person's door for a while, literally and figuratively, saying "Longtemps que je frappe à ta porte" [I've been knocking at your door for a long time], and he's getting a little impatient. He just wants to be close, to feel them near, and he's not afraid to say it: "Arrête de me faire languir" [Stop making me long for you].
He's even making promises, assuring them, "Si tu me laisses entrer, je t'assure, sans me vanter Que tu ne vas pas le regretter" [If you let me in, I assure you, without boasting, that you won't regret it]. He's ready to give his all, wanting to "apprendre à lire en toi" [learn to read inside you] and make them happy. It's a fun, confident, and slightly cheeky song about someone who knows what they want and is determined to get it!