General loudness:
* Très fort: This is the most common and straightforward translation, literally meaning "very strong."
* Extrêmement fort: This means "extremely loud" and emphasizes a high level of loudness.
* Assez fort: This means "quite loud" and suggests a moderate level of loudness.
Specific situations:
* À tue-tête: This idiomatic expression literally means "at the kill-head" and implies shouting at the top of one's lungs.
* À pleins poumons: This means "with full lungs" and suggests a loud and forceful vocalization.
* D'une voix tonnante: This means "with a thundering voice" and describes a very loud and powerful voice.
Other options:
* Fort comme un lion: This means "loud like a lion" and compares the loudness to a lion's roar.
* Fort comme un taureau: This means "loud like a bull" and compares the loudness to a bull's bellow.
The best choice will depend on the specific situation and the desired level of intensity.